Implemented new service interface.

The interfaces for the following services have been created:
- AnswerService
- QuestionService
- FeedbackService
- ReviewService
Changed domain/data model.

- Added IsPrivate field to question and answer.
- Added Title field to question.
- Added FeedbackToken field to QuestionEntity (a one-time toke used to
check if feedback came from the user that asked the question when this
user isn't authenticated).
- A question now has a Answer field instead of a Anser an Question field
and fixed all code that used this.
- Fixed some typos.
- Changed SourceType to SourceDefinition in Question and fixed all code
that used this.
- Made CreationTime a required field in the db.
- Added question field to feedback.
Added language definition.

- Added language definition to answer and question.
- Removed username and password from user, since we're going to use
openId.
Merge pull request #16 from teugis/master

Implemented new service interface.
Added url to source definition.

The url is required to make logging in using an openId provider
possible.
Merge pull request #17 from teugis/master

Added url to source definition.
Bug fix iin Accept answer
Merge remote-tracking branch 'upstream/master'
Implemented answer service
Merge pull request #18 from daanvc/master

implemented answer service
Fixed the answer states so they make sense
Merge pull request #20 from teugis/master

Fixed the answer states so they make sense
Added missing method in IFeedbackService

Fixed typo in IReviewService
Added missing method in IFeedbackService
Fixed errors du to missig Answer states.
Merged Main repo in my fork.
Merge pull request #21 from teugis/master

Added missing method in IFeedbackService
Fixed typo
Merge pull request #22 from teugis/master

Fixed typo
Implemented the question service
Merge pull request #23 from daanvc/master

Implemented the question service
Implemented the updatequestion manager