Replace optparse with argparse, use subcommands

Argparse supports subcommands, which makes it easier to group options
with their related action.

The actions list-applications, list-users, list-craches, add-app-user
and detail are now subcommands.

One downside is that python 2.7 argparse does not support aliases, so no
short versions of the above list are implemented. (previous short options -a,
-u, -c and -d does not have any new equivialent)
Added debian package

Currently only builds for python 2.6

Change-Id: Idba476b8ee981fb789e5e73f4137afa8653f71a1
Don't import in __init__.py

This makes it possible to get the version number without having all of
the required packages.

Change-Id: I6aed75d52724d274e5f762077eea061589e682c4
debian: Also build for python versions above 2.6