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
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
Merge pull request #1040 from ussuri/fix-stuck-menu-selection

Fix sticky menu selection
merge to master