Fixes #1215: Improve the Calendar/Contacts section.

This commit accomplishes the todo items in issue #1215. Specifically:

* Servers and clients are split in italicized sub-lists.
* Link to Wikipedia's article on CalDAV/CardDAV comparisons is added.
* Additional projects are added.

Specifically, the following projects have been added:

* DAVdroid
* EteSync Web

More projects can be added, if desired.

Further, this commit changes the headline from "Calendar and Address
Books" to "Calendaring and Contacts Management" so as to more clearly
describe the purpose of the projects in the list.

README.md

@@ -14,7 +14,7 @@ See [Contributing](.github/CONTRIBUTING.md).
 - [Automation](#automation)
 - [Blogging Platforms](#blogging-platforms)
 - [Bookmarks & Link Sharing](#bookmarks--link-sharing)
-- [Calendar and Address Books](#calendar-and-address-books)
+- [Calendaring and Contacts Management](#calendaring-and-contacts-management)
 - [Communication systems](#communication-systems)
   - [Custom communication systems](#custom-communication-systems)
   - [Email](#email)
@@ -192,21 +192,30 @@ See also [Static Site Generators](#static-site-generators), [Content Management
 - [Shaarli](https://github.com/shaarli/Shaarli) - Personal, minimalist, super-fast, no-database bookmarking and link sharing platform. ([Demo](https://demo.shaarli.org)) `Zlib` `PHP`
 - [unmark](https://github.com/plainmade/unmark) - An open source to do app for links. `MIT` `PHP`
 
-## Calendar and Address Books
+## Calendaring and Contacts Management
 
 **[`^        back to top        ^`](#)**
 
 Some [Groupware](#groupware) solutions also feature calendar/address book editing and synchronization.
 
+See https://en.wikipedia.org/wiki/Comparison_of_CalDAV_and_CardDAV_implementations
+
+_CalDAV or CardDAV servers_
+
+- [Baïkal](http://sabre.io/baikal/) - Lightweight CalDAV and CardDAV server based on sabre/dav. ([Source Code](https://github.com/sabre-io/Baikal)) `GPL-3.0` `PHP`
+- [CalendarServer](https://www.calendarserver.org/) - Apple, Inc.'s standards-compliant server implementing the CalDAV and CardDAV protocols shipped with macOS Server. ([Source Code](https://github.com/apple/ccs-calendarserver)) `Apache-2.0` `Python`
+- [calypso](https://keithp.com/calypso/) - Python-based CalDAV and CardDAV server, forked from Radicale. ([Source Code](https://keithp.com/git/calypso.git)) `GPL-3.0` `Python`
+- [DAViCal](https://www.davical.org/) - Server for calendar sharing (CalDAV) that uses a PostgreSQL database as a data store. ([Source Code](https://gitlab.com/davical-project/davical)) `MIT` `PHP`
+- [EteSync Server](https://www.etesync.com) - End-to-end encrypted and journaled personal information server supporting calendar and contact data, offering its own clients. ([Source Code](https://github.com/etesync/server-skeleton)) `AGPL-3.0` `Python/Django`
+- [Radicale](http://radicale.org/) - Simple calendar and contact server with extremely low administrative overhead. ([Source Code](https://github.com/Kozea/Radicale)) `GPL-3.0` `Python`
+- [SabreDAV](http://sabre.io/) - Open source CardDAV, CalDAV, and WebDAV framework and server. ([Source Code](https://github.com/sabre-io/dav)) `MIT` `PHP`
+
+_CalDAV or CardDAV clients._
+
 - [AgenDAV](http://agendav.org/) - Multilanguage CalDAV web client with a rich AJAX interface and shared calendars support. ([Source Code](https://github.com/agendav/agendav)) `GPL-3.0` `PHP`
-- [Baïkal](http://baikal-server.com/) - Lightweight CalDAV+CardDAV server. ([Source Code](https://github.com/fruux/Baikal)) `GPL-3.0` `PHP`
+- [DAVDroid](https://www.davdroid.com/) - Open-source CalDAV/CardDAV suite and sync app for Android. ([Source Code](https://gitlab.com/bitfireAT/davdroid)) `GPL-3.0` `Java`
-- [CalendarServer](http://trac.calendarserver.org/) - A standards-compliant server implementing the CalDAV and CardDAV protocols. `Apache-2.0` `Python`
-- [calypso](http://keithp.com/calypso/) - A python-based CalDAV/CardDAV server. ([Source Code](https://keithp.com/git/calypso.git)) `GPL-3.0` `Python`
-- [DAViCal](http://www.davical.org/) - A server for calendar sharing (CalDAV). ([Source Code](https://gitlab.com/davical-project/davical)) `MIT` `PHP`
-- [EteSync](https://www.etesync.com) - Secure, end-to-end encrypted and journaled personal information cloud synchronization for Android and the desktop. Currently contacts and calendars, with more on the way. ([Source Code](https://github.com/etesync/)) `AGPL-3.0` `Python/Django`
-- [Radicale](http://radicale.org/) - A Simple Calendar and Contact Server. ([Source Code](https://github.com/Kozea/Radicale)) `GPL-3.0` `Python`
-- [sabre/dav](http://sabre.io/) - A open source CardDAV, CalDAV and WebDAV server. ([Source Code](https://github.com/fruux/sabre-dav)) `MIT` `PHP`
 - [InfCloud](https://www.inf-it.com/open-source/clients/infcloud/) - An open source CalDAV/CardDAV web client implementation. ([Demo](https://www.inf-it.com/infcloud/), [Source Code](https://www.inf-it.com/InfCloud_0.13.1.zip)) `AGPL-3.0` `Javascript`
+- [EteSync Web](https://www.etesync.com/faq/#web-client) - EteSync's official Web-based client (i.e., their Web app). ([Demo](https://client.etesync.com/), [Source Code](https://github.com/etesync/etesync-web)) `AGPL-3.0` `TypeScript`
 
 ## Communication systems