Merge all the templates together, add a few new features to help with the merge.

This merges together all the templates into a single template (still overridable) and adds:

* `keys_enable`, `keys_trusted`, `keys_controlkey`, `keys_requestkey`, `keys_file`: Parameters to let you configure ntp keys
* `driftfile`: Lets you set the driftfile location.
* `preferred_servers`: Lets you set which servers are to be preferred.