Add "cascade" filter run prefix and use it to control view templates (#6168)

* Initial Commit

* Set currentTiddler and ..currentTiddler for filter evaulation

* Precompile the filters for performance

* Add explicit test for empty result when no filter passes

* Use the cascade filter run prefix to choose the view template body template

* Use the cascade mechanism to choose between the edit and view templates

* Simplify cascade filter

Thanks @saqimtiaz

* Add control panel UI for inspecting the template cascades

* Refactor import listing and plugin listing as alternate body templates

As suggested by @pmario

* Refer to $:/core/ui/{View|Edit}Template via their associated config tiddlers

* Fix typo in previous commit

* Add demo of custom story tiddler template

* Tweak control panel wording

* Standardise "Story Tiddler Template" nomenclature

* Add a cascade for the editor template body

* Add a cascade for the view template title

* Avoid unwanted whitespace

* Add a cascade for dynamically choosing tiddler icons

core/wiki/config/EditTemplateBodyFilters.multids

@@ -0,0 +1,5 @@
+title: $:/config/EditTemplateBodyFilters/
+tags: $:/tags/EditTemplateBodyFilter
+
+canonical-uri: [has[_canonical_uri]then[$:/core/ui/EditTemplate/body/canonical-uri]]
+default: [[$:/core/ui/EditTemplate/body/default]]

core/wiki/config/StoryTiddlerTemplateFilters.multids

@@ -0,0 +1,5 @@
+title: $:/config/StoryTiddlerTemplateFilters/
+tags: $:/tags/StoryTiddlerTemplateFilter
+
+draft: [is[draft]then{$:/config/ui/EditTemplate}]
+default: [{$:/config/ui/ViewTemplate}]

core/wiki/config/TiddlerIconFilters.multids

@@ -0,0 +1,5 @@
+title: $:/config/TiddlerIconFilters/
+tags: $:/tags/TiddlerIconFilter
+
+icon-field: [has[icon]then{!!icon}]
+default: [{$:/config/DefaultTiddlerIcon}has[text]]

core/wiki/config/ViewTemplateBodyFilters.multids

@@ -0,0 +1,8 @@
+title: $:/config/ViewTemplateBodyFilters/
+tags: $:/tags/ViewTemplateBodyFilter
+
+system: [prefix[$:/boot/]] [prefix[$:/config/]] [prefix[$:/core/]!field:title[$:/core/readme]!field:title[$:/core/icon]] [prefix[$:/info/]] [prefix[$:/language/]] [prefix[$:/languages/]] [prefix[$:/snippets/]] [prefix[$:/state/]] [prefix[$:/status/]] [prefix[$:/info/]] [prefix[$:/temp/]] +[limit[1]then[$:/core/ui/ViewTemplate/body/code]]
+import: [field:plugin-type[import]then[$:/core/ui/ViewTemplate/body/import]]
+plugin: [has[plugin-type]then[$:/core/ui/ViewTemplate/body/plugin]]
+hide-body: [field:hide-body[yes]then[$:/core/ui/ViewTemplate/body/blank]]
+default: [[$:/core/ui/ViewTemplate/body/default]]

core/wiki/config/ViewTemplateTitleFilters.multids

@@ -0,0 +1,5 @@
+title: $:/config/ViewTemplateTitleFilters/
+tags: $:/tags/ViewTemplateTitleFilter
+
+system: [prefix[$:/]then[$:/core/ui/ViewTemplate/title/system]]
+default: [[$:/core/ui/ViewTemplate/title/default]]