Add print server for label printer to have it easily usable via SSH

Add and configure a print server for the Brother P-touch QL 500 label
printer, so that it can be easily used via SSH.

Do the following to make that work:
- Configure the print server host.
- Package printer-driver-ptouch to have a working driver for the label
  printer.
- Configure CUPS.
- Add a script "forcecommand-lpr-wrapper", which works together with the
  ForceCommand sshd_config option and wraps lpr to provide an easy
  interface to use the Brother QL 500 label printer via SSH.
- Add a print user and configure SSH to have the
  "forcecommand-lpr-wrapper" script accessible without a password using
  the print user via SSH.

config/hosts/ptouch-print-server/forcecommand-lpr-wrapper/setup.py

@@ -0,0 +1,7 @@
+from distutils.core import setup
+
+setup(
+    name = "forcecommand-lpr-wrapper",
+    version = "0.0.1",
+    scripts = ["./forcecommand-lpr-wrapper.py"]
+)