Polymer UI menu: cleanups, refactorings, etc.
Added "change theme" and "change keys" to Polymer UI menu

Might be temporary, if can't make them work.
add error message for grind
Fixed widgets and Polymer UI: menu selection is plumbed up to the UI now
Add Public key to manifest.
Merge branch 'upstream/master'
Addressed comments
Original jobs code (from drake)
Changed the library to spark.app
Added test (changed main to defineTests).
changed comment in jobs.dart
Linted
Merge branch 'upstream/master'
Fleshed out comments.  Clarified parameter name.
WIP: switching to MVC paradigm in Polymer UI

SparkPolymerUI receives a handle to SparkModel, which Spark and SparkPolymer implement. SparkPolymerUI uses the model to map various events in the UI to ActionManager calls, etc.

There is currently a race condition: Spark ctor wants to access various elements of the UI, and so the UI (SparkPolymerUI) gets created too early, before enteredView() fires for various components, leading to a crash in SparkSelector on a null _target.
Merge branch 'upstream/master'
Add assert
Fix unnoticed refactoring artifact
fix an issue with focus and active editors
batch resource change events