Change face cursor and increase padding

Improve visual style.
Install PAM service file

Install PAM service file into sysconfdir.
Install a simple script to run X11 user sessions

Xsession script will be used to start user sessions when X11 support
is enabled.

Issue: #12
Use Xnest when running in test mode

Xnest seems to work better than Xephyr which doesn't have support for
hardware acceleration and this may cause problems to the greeter.

Issue: #12