Add ForwardingKeyProcessor that hooks input for all text views.
Proof of concept: working <Shift+Left> in both VsVim and immediate window.
Working <Ctrl+F>.  Handle more arrow commands.
Insert FallbackKeyProcessor between VsVim and Visual Studio for when disabled.
Upgrade to table-driven fallback binding dispatch.
Retrieve removed bindings from settings.
Add settings changed event and use one fallback key processor for all text views.
Comment fallback key processor and provider.
Map letters by key codes

This switches the processing of letter keys to use key codes instead of
textual input.  The process we are simulating here is the core command
routing of Visual Studio.  This occurs during PreTranslateMessage and
looks at virtual key codes.  Looking at the WPF key entries directly
here gives us the closest behavior.
Only fallback in vim buffer if VsVim disabled

My previous change was simply broken for vim buffers.  It was always
routing keyboard input through the fallback processor.  This fixes this
by only routing to the fallback processor on a vim window if VsVim is
currently disabled
Merge pull request #1 from jaredpar/fixes-925

Map letters by key codes
Merge pull request #1232 from ricksladkey/fixes-925

Fixes #925