* Add icon for view template segment
* Muted background colour for view template segment
* Include links to parent tiddlers in the view template segment
* Fix logic for hiding/showing documents/headings (“open”/“close” were
transposed)
1. Switch from using the text field of lists for storing the associated
filter to using the field `toc-list-filter` (to make it harder to
accidentally parse the text of an ordinary tiddler as a filter)
2. Fix several bugs
