Defined the toast notification service

This change defines the toast notification service.  It still has quite
a bit of work to do but the basic structure is there and it can display
elements at this point
Toast notification service is now theme aware
Switched the vimrc upgrade to a IVimBufferCreationListener
Conflicting key binding moved to toast notification service
Finally got the styling working
Toast control now properly hides
Added a simple unit test
Ability to remove notifications

Added the ability to remove toast notifications.
General purpose close mechanism

The toast notification display now has a general purpose close mechanism
for every notification.  This is now uniform across all notifications
and there is no longer a need to add one for every notification in the
system.
Converted VisualAssist notification to toasts
Moved everyone to common close
Merge pull request #1394 from jaredpar/fixes-toast

Fixes toast notifications