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
Fixed the broken <spark-splitter>

Some recent change in Polymer has changed the way custom elements get registered. As a result of that, and possibly some wrong Polymer usage in Spark, all Xyz.created ctors for Spark widgets were called twice. Calling real initialization from there for SparkSplitter caused a crash on the second call, because _target would be initialized to null for some reason. Redone to use enteredView(), which is probably more correct anyway.
Cleaned up debugging leftovers
Merge pull request #486 from ussuri/fix-spark-splitter

Fix spark-splitter
Merge branch 'upstream/master'
Fixes to file close and rename actions

* Added walkChildren method to workspace containers to traverse all
children of the container
* Closing a project now closes all open tabs which were open
* Fixed _closeOpenEditor so that it called the appropriate editorarea
function
* Added _renameOpenEditor function which renames the tab of a renamed
resource
Reinstated unlink function

In previous commit, closed files or projects weren't unlinked from the
workspace.
Renamed _preOrderTraversal to Container._workspaceTraversal

Also, removed the sorting of the children of the container
Removed trailing whitespace
Changes to reflect code review

* walkChildren() is now defined on all Resources, not just Containers
* renamed FileOrProjectCloseAction to ResourceCloseAction
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.
Renamed Resource.walkChildren to Resource.traverse
Fixed a small bug: itemSelector was initialized to '', but tested against null
Merge pull request #487 from ovangle/close_action

Minor fixes for close and rename actions.