Add zanata-overlay submodule.

This submodule takes care of building an overlay zip file that when extracted on top of the different supported JBoss distributions, will supply the necessary components for Zanata to run. In this iteration it contains:
- Necessary jboss submodules
- Configuration and startup scripts for zanata
- Installation scripts which fetches the war file from the web and configures some parts of the application.

Currently, it builds 2 distributions:
Wildfly 8.1
EAP 6 (6.3 recommended)

This pull request goes hand in hand with https://github.com/zanata/zanata.github.io/pull/13
Wait, I thought the overlay was just a zip to be extracted over the top of a fresh app server.  We can't rename files unless we have an installer script.  Which this obviously is.  

So yeah, make a backup of the old standalone.xml, but I'm thinking this module is misnamed.  It's more like `zanata-installer` than `zanata-overlay`.