Improve error message for missing commands
Updated icons
Fixes to action-deletetiddler widget
More action-deletetiddler fixes
Refine refreshing of tiddler widget

We need to refresh if there is a change in the state that we copy to
variables.
Fix problem with blank values in action-setfield widget

One manifestation of this problem was that it wasn’t possible to use
the edit template to add a field without specifying a value
Improve detection of modified drafts

If the target tiddler of the draft is missing (as happens after
clicking “new tiddler”), then we count the draft as modified if the
text is not empty.

Also we count the the draft as modified if the draft title has been
changed
More resilience to Tiddler.isEqual()
Smarter cancel edit behaviour

If we cancel editing a tiddler that doesn’t exist, then we no longer
show the resulting missing tiddler.