Use Setuptools to build gajim

Closes #8633

See merge request !128

If io_add_watch is available like on Linux, the PROCESS_TIMEOUT,
is only used to check for timed out events.

On Window its also used to call select() on the socket, so we get
pending data. We need this as low as possible otherwise Gajim on
Windows feels painfully slow.

otherwise we might ship outdated files

Fixes #8673

Use GNotification instead of pynotify or dbus

See merge request !130

# Conflicts:
#   gajim/gajim.py

implement XEP-0380. Fixes #8734

Closes #8734

See merge request !133