vim: some new bundles
gitconfig: various tweaks

- Added some aliases
- Use system-wide meld as difftool (instead of custom build)
- Use terminal vim as editor instead of macvim.
bashrc: Changed path of completion scripts

Now using homebrew git, changed the completion paths to reflect this.
vimrc & gvimrc: Updated config for airline

Now using vim-airline, so tweaked some settings.
vim: updated bundles