Minor clean ups
Fix sticky menu selection

Selection emained after a menu item click and was shown on the next menu opening.

The main reason is a bug in Chrome that fails to remove the :hover style from an element when that element is clicked and programmatically moved out from under mouse in some way. In our case, the menu auto-closes on a click, so the item remained in the :hover state. A solution was to use own CSS class and switch it on/off on mouseover/mouseout events.
Merge branch 'upstream/master'
Merge branch 'origin/fix-stuck-menu-selection'
Fix introduced CSS problems
Fix menu selection not working after dart2js
Fixed a wrong element id
Fix bug in push when the remoteHead is null.
Merge pull request #1046 from dart-lang/fix_in_push

Fix bug in push when the remoteHead is null.
Show keybinding in main menu
nit variable rename
Merge pull request #1048 from sunglim/menu_hotkey

Show keybinding in main menu.
Addressed my own comments from PR #1048 + more minor changes in spark-menu-item
Merge pull request #1050 from ussuri/comments-for-#1048

Addressed my own comments from PR #1048 + more minor changes in spark-menu-item
Merge branch 'upstream/master'

Conflicts:
	widgets/lib/spark_menu_item/spark_menu_item.css
	widgets/lib/spark_menu_item/spark_menu_item.dart
	widgets/lib/spark_menu_item/spark_menu_item.html
fix an issue with polymer and dart2js treeshaking
Merge pull request #1040 from ussuri/fix-stuck-menu-selection

Fix sticky menu selection
review fixes
merge to master
Merge pull request #1054 from devoncarew/devoncarew_fix_menu_polymer

fix an issue with polymer and dart2js treeshaking