Feature question catalogue

This feature adds the option to create multiple questions for one hashtag. The session owner can switch between the questions via a header bar. It is allowed to enter "invalid" data, for example an empty question text.

The validation is now done by the header template and it is not possible to go beyond /readconfirmationrequired if one or more questions have still invalid data.

There is a parsing function which should convert the "old" question data to the new scheme (implemented by this update). Nethertheless it is recommended to start a new hashtag session.

The members of the quiz session cannot switch between questions. There is a timer while the quiz is running which automatically starts the next question after the previous question has timed out.