Rename for code clarity
Centralized the key event state
Added some unit tests for key events
Removed StatusLine dependent property

This was really adding no value to the code here.  It was serving
instead as a distraction as it made it hard to discern that
CommandLineTextBox.Text and StatusLine were the same value
Better way of updating command line
Underlying mechanism for ctrl+r now supported

The underlying object model of vim now supports ctrl+r.  Need to make
some changes so that this can be surfaced in the UI
Command mode now exposes paste API
Got basic paste working

Lots of work to do here but the basics are working at this point
Paste now works with search
Paste during edit is working

Still some details like getting the " to display.  But overall it is
working great at the moment.
Fixed a broken unit test
Got the " inserted correctly
Merge pull request #1399 from jaredpar/fixes-551

Fixes 551