Reuse existing draft if available when switching a tiddler to edit mode

Fixes #199
Allow field modules to specify HTML element tag used for editing
Extend tiddler modification and creation dates to include milliseconds

Fixes #200
Refactored CSS classes for tiddler titles

Now we reserve the `title` class for the tiddler title span itself, and
`titlebar` for the previous purpose of identifying the div containing
the title and the toolbar buttons
Restore the zoomin storyview

Now we fix the tiddler width properly.
Merge backlog of changes from master branch

This is too easy. I'm worried.
Merge pull request #178 from Jermolene/widgets_redux2

Rejigged Widgets Redux - finally. Couldn't come soon enough.
Move the widgets back to the right folder
Change `new_widget` to `widget`

I was avoiding doing this until after the merge.
Get rid of the "new_" prefix we had on some methods

There's still the "old_" prefix to get rid of too.
Make sure external links have the class "tw-tiddlylink-external"

Fix #203
Docs updates
Make the zoomin storyview visualisation properly track the title node
Fixed typo
Rearrange misplaced docs
Fix up classes for missing tiddlers
Update `tw-new-tiddler` message to take a template tiddler

The template tiddler title is used as the basis of the new title, which
is probably not very convenient. We'd like to be able to use system
tiddlers as templates, without defaulting the new instance to a system
tiddler title.
Docs updates
Add docs for 5.0.0alpha11
Version format update