Configure nginx to run properly under supervisord

Don't daemonize. Use exec in startup script.
Get postgres working properly with supervisord.

supervisord fails to shutdown postgres cleanly when it's run using
`su omero -c "$PGBIN/postgres -c config_file=$PGCONF"`
because su starts another shell which means the QUIT signal doesn't get passed to postgres. E.g.

2014-08-11 15:11:06,560 INFO waiting for pgsql to die
2014-08-11 15:11:08,563 WARN killing 'pgsql' (133) with SIGKILL
2014-08-11 15:11:08,563 INFO stopped: pgsql (terminated by SIGKILL)

Note `su omero -c "exec ..." doesn't work either. The user to run postgres is now set in supervisord.conf, but to allow auto-creation of the database data dir (which must be run as root) a one-time setup script has been added.
Split omero supervisord startup into root and non-root commands.

As with postgres use the supervisord user switching capability instead of `su -c`.
Fix wait_on_postgresql to use the correct data dir
Incorrect branch, OMERO-5.0-latest-build should be OMERO-5.0-latest
Run web using the omero user in supervisord
Tidy up priorities (leave space for other extensions)
Forgot to add new files to Dockerfile
Include /etc/supervisor/conf.d/*.conf

This makes it easier for other containers to extend this one.
Add "$@" to /supervisord

Useful for testing, e.g. you can start the container and pass "-e debug" to get debug logs
Add pytables to omero-base
Use default TERM instead of QUIT signal

QUIT causes omero and web to core-dump.
Merge pull request #2 from manics/omero-in-a-box-exec-fixes

Omero in a box exec/user fixes