Parse :only
Began to implement :only

Still need to:
- Manually test
- Fix VimApp
Made the Vim App conform to the interface change

I have yet to figure out what the appropriate way of actually
implementing `:only` and `:tabonly` for the Vim App is.

Also, did the manual testing for `:only`.
Merge pull request #1459 from Kazark/master

Implement :only to be the same as :tabonly for now
Added the explicit interface implementations

I missed this when I was reviewing the recent changes in this area.

I should probably elaborate on why I actually have this practice because
I'm sure it's not a popular one: in short I find that it is a code
maintenance win.

VsVim is a decently sized project at this time and it's easy for code to
get stale over time.  Before I used explicit interfaces I kept finding
dead code which used to implement interface methods (which had
themselves long ago been deleted).  I constantly found myself spending
considerable time trying to update algorithms and decipher old code only
to find that it was dead code all along.

Using explicit interfaces helps combat this.  If an interface changes
there is no way that it will silently impact an implementation now.  It
will force at least a casual glance at the implementation to see if it
is relevant or not.

Generally I don't care as much about this when an interface has 1 or 2
methods.  But past that I'm pretty rigid about explicit implementations.
Fix matching token

closes #1362
Remove Visual Studio phrase from host API

Remove the phrase VisualStudio from the host API.  The core layer should
have no knowledge of VisualStudio because it's a specific host.
Removing the phrase from the API to make that a bit clearer to others
Fix a build issue
Remove VsixUtil source

VsVim will now use VsixUtil as a nuget package.  VsixUtil originated as
a tool for VsVim but now it's used on more VSIX projects.  Don't want to
duplicate the source hence removing it