Powerline configuration for work linux

Enables powerline fonts, airline prettiness as well as mouse.
Convert setup.sh URIs to https

This is so we can actually install remotely from anywhere, instead of
relying on having ssh keys setup.
Remove Lokaltog/vim-powerline from Bundle list

powerline was interfering with and was superseded by vim-airline.  For
whatever reason vim-powerline turned into a large Python fancy prompt
system.
Make airline powerline font env conditional

Looks for a $POWERLINE_FONT environment variable to be set before
turning on powerline fonts in vim.  Maybe this will allow me to use one
branch between all my environments.
Pull from a specific git branch when updating

For compatibility with git 1.8+
BundleClean! before installing during update

After an update, Bundles were being left in their respective folders.
Cleanup, then install.
Fix and label Markdown augroup
Only turn on mouse support if available
Turn on search highlight by default
Update vundle to the latest Vundle.vim spec