Added colored prompt when "sudo" is not expired.

Show the prompt in yellow when you can use sude without providing a
password (when the sudo session is not expired). In addition colors
for the prompt are changed to use the standard colors provided by
the terminal color-scheme (or at least partially).
Added markers for git branches that have diverged.

Check whether the branch is both ahead and behind, in this case the
tracking branch has diverged from its remote counterpart.
Changed some of the markers for git branches.