Scripts update

This PR contains

- a small update for the `bin/update.sh` script
- a complete rewrite of the `bin/sockets.sh` script.
- an init.d script

## About the sockets:

- instead of having a cron job running every minute to restart the sockets.sh script, the script should be started only once. It keeps on running until it is killed using `^C/SIGINT`, `SIGTERM` or `SIGQUIT`.
- running `bin/sockets.sh` twice will not result in starting the sockets twice: the second call will send `SIGUSR1` to the first script, which restarts the sockets.
- the script in `bin/init.d/litus` is an init.d script for litus. It will create the necessary directories at boot time, start the sockets and the printers (if needed) and can be used to query the status of the daemons or stop/restart them.

### Long story short:

- Installation
  - run `php public/index.php install:common` to install the necessary configuration entries
  - update the configuration entries for `socket_path` and `socket_log`, the default values should be OK for a host with only one Litus instance
  - __symlink__* the init.d script to `/etc/init.d/litus` and run 
`
sudo update-rc.d litus defaults 99
`
  - reboot the server/computer or run `sudo service litus start`
- Configuration
  - the default configuration works for a single Litus system without printers.
  - the Litus service can be configured by creating `/etc/default/litus`:
```bash
USER=<username, default is www-data>
LITUS=<space separated list of repo root directories of Litus installations>
HAVE_PRINTERS=<number, 0 (default) is off, 1 is on>
```
  - the `socket_path` and `socket_log` configuration entries control where the pid files and logs of the sockets will be written.

### init.d actions

- `service litus start` starts the sockets (and printer daemon if enabled)
- `service litus restart` sends `SIGUSR1` to the sockets, restarting the sockets but not the governing script, it also restarts the printer daemon if enabled
- `service litus force-restart` the same as running stop then start
- `service litus status` prints information about the state of the sockets and printer
- `service litus stop` stops the socket script and the printer daemon

### Notes

- Currently blocked on doctrine/DoctrineModule#400
- Using the printer daemon requires `/opt/litus/PrintDaemon.jar`

*: if you want to copy (which is more secure, because you can chown to root:root chmod 755) you'll have to fill in the `LITUS` variable in `/etc/default/litus`. This variable defaults to `$(dirname $(readlink -f <path of init.d script>))/../..`