Add Gdash module; remove Gdash source tree from Puppet

This change converts the web app powering http://gdash.wikimedia.org/ to use
the git-deployed Gdash, configured as part of change I4c088cf5e.

Remaining TODOs:

- Document gdash class parameters.
- Provision web server configuration, too.
- Create a 'dashboard' resource & use it to declare dashboards.

The ordered_json() function in modules/gdash/lib is a direct copy of the one in
the StatsD module, duplicate to prevent a hidden dependency relationship. It
should probably be moved into a separate module ('wmflib'?).

Change-Id: I13128f794e1a87b0535e9b7ff05c24303b034cee
Merge "Add Gdash module; remove Gdash source tree from Puppet" into production