Ubuntu 14.04 support.

This Pull Request adds Ubuntu 14.04 support. Two things to note:

- The nginx cookbook does not support Ubuntu 14.04 yet because of a change pidfile location. See https://tickets.opscode.com/browse/COOK-4685
- The postgresql cookbook does not support Ubuntu 14.04 with the newer PostgreSQL 9.3 version yet. So the Cheffile contains a pointer to our own postgresql fork:  https://github.com/intercity/cookbooks-postgresql