Merge branch 'feature_session_info' into 'master'

WE Offshore Sprint: Session Info Feature

We had the task to implement a Session-Info Form, where the speaker
could add more information to a session, which is already created or to
add more information to a session which is created at that moment.

Therefore we needed to use the update Method and change some code in the
backend as well:

1. Changed **updateSession** Method in SessionService
  * First: we get the session that should be updated from the DB with
    the getSessionFromKeyword-Method
  * Second: we update the values of the session with the new values that
    were entered
  * Third: we check the logo just like in the saving Method of a session
  * we return the updated session
2. Changed **getSessionFromKeyword** Method in CouchDBDao
  * We added these fields, so that they are also fetched:
     * ppAuthorName
     * ppAuthorMail
     * ppUniversity
     * ppLogo
     * ppSubject
     * ppLicense
     * ppDescription
     * ppFaculty
     * ppLevel

See merge request !7