reverted build process to single file pattern; broke remaining "plugins" files into their own full-fledged plugins.
Removing tangelo.widget() function (and tangelo.unavailable())

"Tangelo widgets" are now just regular JQuery widgets.  The magic of
interpreting objects as tangelo accessors no longer happens automatically; users
will either call tangelo.accessor() to manufacture a function, or else supply
their own functions directly.
Merge branch 'remove-tangelo-widget' into plugin-system