Add optional templating for the register site aspect of a pillar.
User can specify keys to be included as defaults, otherwise it is
treated as a normal managed file.
When using the register_site state, if the `state` for the
site in the apache pillar did not equal "enabled" the error
```
Cannot extend ID 'a2ensite <name>' in 'base:apache.register_site'. It is not part of the high state.
```
If statements were there to build out the `a2ensite` or `a2dissite` ID
appropiately, but the next state for managing the config always
assumed that the `a2ensite` id would be there.
Addressed by making a Jinja variable that will be the appropiate ID,
probably could use a better name.
