Restore focus to ITextView for commands

A good portion of Visual Studio commands expect the focus to be in the
editor when they are run.  Some code paths in VsVim had the focus else
where, like the command margin.  This change forces the focus back to
the editor for all commands
Fix key map with arguments

At the moment VsVim doesn't fully support key mapping options like
<silent>.  Rather than ignoring the option and continuing though VsVim
completely blocked the key mapping.  Switched the behavior to allow the
mapping.

closes #1368