Add banner for binary tiddlers in edit mode

Makes it easier to add tags to a binary tiddler (eg a PDF).
Remove dead code typo
Start adding support for permalinks

At this point we respect any permalink at startup, but we don’t yet
dynamically update the permalink, nor do we respond to ongoing
permalink changes.

The permalink separator being `%00` seems like it might be a bit
controversial. It buys us not having to wrap tiddler titles in double
square brackets if they contain spaces.

Another thing is that this scheme doesn’t support tiddler filters; the
plan is to support them like this:

http://tiddlywiki.com/#!Target%00%00[tag[task]sort[created]]