Tab / Backspace handling has option

The tab and backspace commands now have a concrete option to decide
whether they should have Visual Studio or Vim behavior.
gVim 7.3 is the new default

This ended up causing too much negative user feedback.  The good news
though is this is a setting now hence it's super easy to change.  If
people want 7.4 it's a click away
Simulation tests for the new option
Changed vimrc load behavior

The loading of vimrc files is now disabled by default.  Loading of
vsvimrc files remains unchanged.  Going to write an option here in a bit
that allows opting back into loading vsvimrc files
Fix unit test failure
vimrc filtering is more flexible now

This change gives the host total control over loading the vimrc file.
Can choose from vimrc, vsvimrc, both or none
Fixed the options display

Now the description is displayed instead of the simple value
DefaultSettings wasn't being respected
Merge remote-tracking branch 'origin/master' into fixes-settings
Removed ILegacySettings

It's been over a year since we transitioned away from application
settings.  No need to keep the migration code around anymore.
Got the TODO up to date
Host customization of global settings
All host options now have a UI element
Description update
Removed unnecessary field
Revert "Removed unnecessary field"

This reverts commit 8b3ed3eecbdab90866f29815232a69122c7b2105.
Made new line indenting host overridable
Cleaned up the setting sync API
Made sync completely host overridable
Added ability to add custom settings