A new colour palette
Improve handling of popup state

An improvement to 6fb992690d33940d3509d7d4d74538e7f458e063

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).
Docs updates