* UIMG and UOPN require the client to specify a Mimetype now.

* UIMG and UOPN require the client to specify a Mimetype now.
* the list file now contains this mimetype too, if there is no statement with a '/' in the expected place, we fallback to old notation and specify application/octetstream
* adjust the client library.
* in rooms.c list the [mimetype]. if s.b. doesn't like this notation, please change.