Correct misspelled class name.
Remove unused imports.
Add Hibernate Validation to Gutterball.
Merge pull request #765 from candlepin/awood/gb-validation

Awood/gb validation
Added the status trend report and API.

- Report supports filtering by date and any one of: sku,
  entitlement name or the management_enabled entitlement
  attribute.
- The database query and general data gathering is performed
  by the ComplianceSnapshotCurator.
- The request is processed by the StatusTrendReport class.