Load external completion files

* Bash completion for git is now loaded from the git installation
  itself, so I don't need to copy it here.
* Same for git prompt.
* Added loading of completion file for homebrew.

Other small fixes and cleanups:
* Moved aliases into .bashrc
* Moved editor export into .profile
.bashrc: Aliases for PostgreSQL

Added aliases to start and stop the local PostgreSQL server.
PATH: Prepend homebrew binaries dir

Homebrew binaries should be found before the system binaries.
New vim plugins: bash-support, c-support and taglist