adding fancy bash Git prompt

from https://github.com/magicmonty/bash-git-prompt
removing ECG settings as not used anymore
as we are always using emacs 24 now, removing the condition

also setting up system variables for proxy settings
el-get packages cleanup (a bit)
when trying to contact Twitter from emacs, use other browser than w3m

Twitter doesn't handle well that browser
cleanups
fixing up slime setup, as we don;t use slime-js
cleanups