sync: support renames and deletions

[FND]

Recent work on server-side saving has introduced new conventions for detecting renames and deletions (using extended fields* as flags).

The synchronization wizard should support these conventions and adjust the synchronisation status message accordingly.

* tentatively called deleted and originaltitle

[FND]

N.B.: TiddlyWeb's adaptor currently uses tiddler.fields.originaltitle, whereas ccTiddly uses tiddler.fields["server.id"]. This needs to be consolidated (e.g. by using tiddler.fields.["server.tiddlerTitle"]).

[FND]

This patch changes the sync wizard's status messages, but still triggers putTiddler for all local changes (rather than supporting renameTiddler and deleteTiddler).

[FND]

Rather than making the core aware of these custom fields (i.e. introducing/enforcing new conventions), it might be considered delegating this to plugins by providing hooks as necessary.

[MartinBudden]

Milestone 2.6.2 deleted

[cdent]

TiddlySpace? has further changed the custom fields, so there needs to be some agreement...