Initial polymer widgets

Added toolbar, icon, icon-button, toggle-button, selections,
menus, and overlay.  Only hooked up toolbar and icon-button need notion of
spark-ui as outermost widget for proper lifetime.  Contents of sparkpolymer.html
will contain <spark-ui> spark-ui template will contain all the UI (TBD).

Overlays and menus will be hooked up next to replace existing menus.

Changed call to initPolymer to call run so proper zone is hooked up so
observable changes are handled.