Debian packaging

This includes packaging for Debian based distros and has been tested with lintian.  There are some warnings, although they're not especially important:

W: pybitmessage: extra-license-file usr/share/applications/pybitmessage/pyelliptic/LICENSE
W: pybitmessage: extra-license-file usr/share/applications/pybitmessage/socks/LICENSE
W: pybitmessage: binary-without-manpage usr/bin/pybm