CouchDBDao:
 * Removed obsolete method currentTimestamp()
 * Explicit IOException catch that indicates communication error

UserService:
 * Log if store file could not be created

Conflicts:
	src/main/java/de/thm/arsnova/controller/QuestionController.java
	src/main/java/de/thm/arsnova/dao/CouchDBDao.java
	src/main/java/de/thm/arsnova/dao/IDatabaseDao.java
	src/main/java/de/thm/arsnova/entities/Question.java
	src/main/java/de/thm/arsnova/entities/User.java
	src/main/java/de/thm/arsnova/services/IQuestionService.java
	src/test/java/de/thm/arsnova/controller/LoginControllerTest.java

Task #4027: getQuestionById fixes if a list of answers exist which could
not morphed by self

The new NoContentException should indicate, that there is no error, but
the server could not provide a response object. This will result in
HTTP Code 204 - NO CONTENT => see RFC2616

Fixed two NullPointerExceptions wich might occure in QuestionService or
by using CouchDBDao from QuestionService.

This change is needed due to client developer restriction not to round
returned value on client side but on server side, because this would
change sth.

This change is needed due tu websocket security issues.

Method SessionService::broadcastFeedbackChanges is obsolete since this
method is used in FeedbackService.

FeedbackService::broadcastFeedbackChanges must not be annotated with
"@Authenticated" since authentication is not implemented for web sockets.

check if session has this question and throw unauthorized exception if
not

add type of user account
adjust test for new user account type
UserServiceTest which test persistence of the maps

Added menu for "Documentation" containing a list of dependencies, a small
indroduction how to install ARSnova for development usage and a link
to generated API docs.

Conflicts:
	src/main/java/de/thm/arsnova/controller/SessionController.java
	src/main/java/de/thm/arsnova/dao/CouchDBDao.java
	src/main/java/de/thm/arsnova/dao/IDatabaseDao.java
	src/main/java/de/thm/arsnova/services/ISessionService.java
	src/main/java/de/thm/arsnova/services/SessionService.java
	src/test/java/de/thm/arsnova/dao/StubDatabaseDao.java