Refactoring

- cleaned up exceptions, created generic exceptions for entity CRUD errors
- consolidated models reported in these exceptions under a BridgeEntity marker interface
- renamed BaseController session methods for clarity
- consolidated StudyControllerService to BaseController and moved it to be a normal service named StudyService
- deleted unused ExceptionInterceptorAction
- renamed post JSON field constants for consistency
- moved fromJson() methods to use JsonUtils for better exception/error case handling
- moved validation out of StudyConsentForm to the StudyConsentService for consistency
- removed role check from UserAdminService. Role checking will happen in controller if one is created