add 'creator' field to tiddlers

[EricShulman]

Currently, when a new tiddler is created, it is automatically assigned field values for 'created' (timestamp) and 'modifier' (==config.options.txtUserName). Subsequent editing of the tiddler adds another timestamp value for 'modified', and replaces the value for 'modifier', using the *current* value of txtUserName

For some use-cases, it is important that the name of the original author of the tiddler is identified and retained, even after that tiddler has been edited by someone else.

 http://www.TiddlyTools.com/#CoreTweaks addresses this by adding a separate 'creator' field to each NEW tiddler, when that tiddler is intially saved to the store. This value remains unchanged during subsequent edits.

In addition, the tweak provides an *option* (chkForceCreatorField) to add a creator value when editing an *existing* tiddler that does not already have this field defined (perhaps because the tiddler was imported from another document where the 'creator' field tweak has not been applied). By default, this option is FALSE, so that ONLY newly created tiddlers will have a 'creator' value assigned.

[mahemoff]

FWIW this is an important requirement for certain TiddlyWeb apps/plugins. e.g. if someone adds a vote or comment, the interesting thing is the creator, not the modifer who is likely to be an admin, since those things are typically create-only for ordinary users. Furthermore, the custom "creator" field workaround would allow people to push in fake data.

[MartinBudden]

Fixed in changeset:11290