Fix for Find UI active but not focused

When the incremental find UI, added in VS 2012, is active but doesn't
have focus then VsVim should be handling the input normally.  It was
incorrectly believing the UI had keyboard focus and hence was just
processing keys as if VsVim wasn't active

closes #1260
Space now works in peek window

The space key now works properly in the peek window.  However there are
still some selection issues.

When the peek window is open there are actually 2 ITextViews for the
same ITextBuffer.  This happens because VS will open the peeked document
as a separate entry.  The selection is being mirrored by VS or VsVim,
unclear which, but not cleared properly.  This leads to the hidden
buffer having a selection but not the active buffer but VsVim keeps
believing there is a selection and hence keeps pushing the peek window
into Visual Mode.

related to #1207
Fix peek window selection issue
Merge pull request #1263 from jaredpar/fixes-focus

Fixes focus