bashrc: discourage use of rm

alias it to echo a message advising the use of trash-put instead.
\rm can be used if I really want to use rm.
emacs: embrace helm

use it instead of ido for find files and switch buffer.
use helm-show-kill-ring instead of browse-kill-ring
use helm-M-x instead of regular M-x or smex
emacs: re-enable vc-git

still use magit instead, but there's no need to disable it.
emacs: use helm-gtags instead of ggtags

bind M-. to find tag and M-, to find rtag