Re-synced with spark.html #2
Merge pull request #371 from dart-lang/fix-polymer-ui

Re-synced with spark.html #2
Midway through intaking recent changes in non-polymer UI

CSS done, everything works. Expecting more CSS changes necessary after syncing HTML.
Make polymer_elements a direct dependency (was indirect via spark_widgets)
3/4 of the way through intaking recent changes in non-polymer UI

HTML done, but widgets are still broken, to do next.
Merge branch 'upstream/master'

Conflicts:
	ide/app/spark_polymer.html
Fixed widgets (superclass Widget moved from src/ to common/)
Fixed path to background image
Fixed mistakenly quoted CSS property value
Fixed the toolbar + minor style fixes - the UI looks normal again