Rt - role to install RT and a number of extensions

Nigel - can you test this ansible play on a new RT server for me?  It's potentially going to need some more work, but I'd like you to test this out first please.
This is great, but remember, this will be run every time you run the RT role. Ansible configuration is supposed to be idempotent. Can we have something to check if RT is installed and if it is, don't do these steps?