Command margin colors exposed in settings

This changeset exposes Command Margin color settings in the Default option page of VsVim.

The default black-on-white scheme is blazing on dark themes.
I thought there's nowhere to set the color before I dig into the code, actually.
So I guess it's better to make it more obvious.

About the Filesystem change: sorry I guess it's BOM related.. doesn't compile here so I changed that character. Please ignore that.