Previously we were using a message `tw-auto-save-wiki` to trigger an
autosave. The message was generated by certain UI actions such as
saving a tiddler. The trouble was that the message was being processed
before the wiki change event for the accompanying change had had a
chance to percolate. The end result was that the dirty indicator was
staying lit when using autosave.
The new approach abandons the autosave message and instead triggers the
autosave in the wiki change event when a relevant change occurs.
One happy side effect of these changes is that the dirty indicator now
works as expected with the client server edition - ie, when typing in a
draft tiddler the dirty indicator will flash briefly, and then clear
when the sync mechanism has completed saving the draft.
We re-use some of the existing syncer mechanism. It was already keeping
track of changes to tiddlers in the store when working with a tiddler
syncadaptor. Now it also tracks changes when there is no syncadaptor,
allowing us to provide a warning if there are unsaved changes.
