Remove spark-select

spark-select has run its course. It was an earlier attempt at widgets and is now replaced by spark-selector.
Right-click on a file will open the context menu (fixed #412)
When no tabs are shown, show the edited filename in the toolbar (fixed #417)
fixed alignement of filename and icon
Fix wrong library locations for grind doc.
Removed todo
Merge pull request #413 from dinhviethoa/412-context-menu-with-right-click

Right-click on a file will open the context menu
Improved toggling label
Merge pull request #418 from dinhviethoa/417-show-filename-when-needed

When no tabs are shown, show the edited filename in the toolbar
Remove unwanted comment
Merge pull request #422 from sunglim/fix_grinddoc

Fix wrong library locations for grind doc.
Merge pull request #423 from dart-lang/fix_polymer

add the zone exception handling to the polymer version
Reflect the true nature of a var through a better name
Merge pull request #426 from ussuri/fix-var-names

Reflect the true nature of a var through a better name
fixed polymer with latest checkin
Merge pull request #427 from dart-lang/menus

fixed polymer with latest checkin
Merge pull request #410 from ussuri/remove-spark-select

Remove spark-select
remove Spark singleton