Reporting API Framework

Details the beginnings of a Report API framework.

ConsumerStatusReport will get another rev after this is merged in and currently returns static data.

Please focus how reports will be created. Need to make sure this is pretty straight forward and relatively easy to do.

NEED TO BE DONE, NOT IN THIS COMMIT
* Exceptions and mappers need to be merged into candlepin-common so that they can be reused here.
* Currently ReportParameters are purely for providing parameter info when requesting report details -- It would be nice for them to contain validation code for each so that we wouldn't need to implement a validation method.
It might be worth having a more general parameter validation method defined in Report.java, which checks that all mandatory parameters are provided, and all non-multivalued parameters have no more than 1 value.
We could call that before the validateParameters defined in the subclass.