Introduction of Stateful#observe(), refs #178, fixes #182.

Also replaces delite/Invalidating with decor/Invalidating, which has a slightly
different API.
Fixes related to Stateful#observable() changes, refs #182.
refactor FormValueWidget test
jshint fixes
added doctype to polymer func test, fixes #225.
convert CssState to use observe() rather than watch(), refs #182.
convert template.js to use observe() rather than watch(), refs #182.