Vim: force 256 color mode for colorscheme

It's possible that color schemes running on linux/ssh may have been
running in low-color (16 color) mode. We've added a command to
hopefully force 256 color mode.
Vim: update Powerline path for linux

Instead of using the Mac homebrew pip install path location for
activating Powerline for Vim, instead use the Linux (local) location
for pip.