Remove solarized folder to prepare for submodule addition

I'll be making the vim-colors-solarized folder into a submodule. In order to do that, I first need to remove the folder from the git index.
Add solarized submodule

This will pull the solarized colorscheme from the official Github repo for vim (maintained by altercation). (Simply pasting the solarized files into the bundle folder doesn't commit them to git correctly.)