More measure exploration

Not yet sure if this typing model is practical or consistent
Unify assetCreate and assetEdit and underlying forms
Make Login a SiteController
Dynamic access to measure data

Oh the precarious typing.  Not sure yet how this should be used.
More documentation on measures and higher-level interface
Add Study.slotRecords to get slot category values
Forget about measure audit for now; add fk actions

Measure auditing is questionable and overly complex.  A flatter solution may be
better, if any.  No auditing for now.
More measure/record stuff, some manipulation

Still not sure if this *Base pattern makes sense, or if a [+T]/[Any] approach
would be cleaner.
Improve syntax and concision with context bounds
Use and cache ident measure on record for sorting
Rework permissions

Attempting to generalize for records/measures, but still not happy with it.  It
does at least seem simpler this way.
Merge remote-tracking branch 'remotes/origin/master' into gui

Conflicts:
	app/controllers/asset.scala
	app/controllers/site.scala
	app/views/asset/create.scala.html