Updated AuthorizationHandler.

Logic for matching users will be added soon.
Added attribute for method-based user authorization.
Removed AuthorizationHandler from BaseManager.

The authorized user can now be retrieved using
AuthorizationHandler.AuthorizedUser.
Processed comments by teugis.
Corrected typos.
Removed some unnecessary variables.
Now allows authorization of multiple user types.
Merge pull request #36 from Plenkske/master

Review methods in new classes, also tests
Added todos and added feedbackToken parameter

- Added todos in ReviewServiceTest class
- Added todos in AnswerManager
- Added feedbackToken to IFeedbackService, FeedbackService and
FeedbackManager
- Updated summary of feedbackToken in QuestionEntity.
Updated AuthorizationHandler.
Added AuthorizationRequired and AuthorizationOptional attributes.

User matching and user creation implementations will follow.
Updated authorization attribute classes.
No longer expecting to receive exceptions.
Updated StringCheck (now also checks for whitespace-only strings).
Better error handling.
Merge pull request #37 from jorisvervuurt/master

Updated BaseManager, added Attribute for method-based user authorization, updated AuthorizationHandler.
Merge pull request #38 from teugis/master

Added todos and added feedbackToken parameter
Added content parameter to UpdateAnswer.
Sorted usings.
Added Issuer property (contains the issuer that provided the user info)