tiddlyweb: add 'creator' field to tiddlers

[mahemoff]

This is the tiddlyweb edition of  http://trac.tiddlywiki.org/ticket/471 .

Both tiddlywiki and tiddlyweb need a "creator" field, but it's possible for each to implement it independently of the other, hence a separate ticket. The independence is because tiddlyweb will ignore the incoming data and apply its own value.

From IRC: cdent: the change we're talking about is adding a creator field to the Tiddler

cdent: we would read from disk to get most attributes, then look at the first revision's modifier and set creator to that cdent: then in the serializations we'd add creator as an attribute that is out put cdent: (json and wiki being the ones that are most relevant)

The requirement is important for Tiddlyweb features involving create-only policies, such as comments and voting. In these situations, the modifier (which *is* available at present) is likely to be an admin, so it's of less interest than the original creator.

[cdent]

this is done with

 http://github.com/tiddlyweb/tiddlyweb/commit/21e980497143966a70cb0aefa48364e98f854515

please let me know if this looks satisfactory

[cdent]

assuming satisfactory, it's been out for quite a while now