Removed vimshell (yet again) see notes

While VimShell is really cool and robust for what it is, it's just not
robust enough to support my regular workflow inside of vim. In
comparison, it's very easy for me to pop terminals with <leader>gt and
not have to worry about cd issues and also C-xC-e will let me edit bash
commands directly in vim which is probably the coolest thing about
VimShell.