An improvement to 6fb992690d
By making sure that all the popup state tiddlers have the prefix
$:/state/popup/ we can be more selective and just exclude popup state
tiddlers when we save. The end result is that once again other kinds of
state are persisted as expected (eg tabs, and sidebar visibility).
By rearranging the `[all[]]` operator we are able to ensure that shadow
tiddlers get processed before ordinary tiddlers. This makes it easier
to create custom stylesheets that override the core.
Add a dropdown for choosing available images for a tag.
As part of this change we need to tag tiddlers that contain images
typed as wikitext (these are inline SVG icons) so that we can display
them in the dropdown.