Added window navigation support to the host application
Changed quick fix API to return a bool

In the current implementation there was no way to report failure.  It
now reports with a bool
Added gt, gT and the like support to VimApp

This changed added support for the tabbing APIs to VimApp.  As part of
this change all of the vim logic around tab indexes and wrapping counts
was moved into VimCore.  The host now just has to implement some very
simple non-vim specific APIs.