sequence number not displayed in communication diagramm (#335)

Hello Dusan,

thank you for implementing most of my requests in 6.60. Great job!

I've got a new one for you so that you won't run out of work ;-)

In a communication diagram, when I add a message between two Lifelines, the diagram does not display the sequence number of the message.

As a workaround, I can add the sequence number to the name of the message, so the problem does not have a high priority.

I also suggest a way to make entering the sequence number easier (currently, it has to be done in the properties dialog): When I edit the message label and enter something like "x y", it should set the sequence number to x and the message name to y.

Thanks,

Mathias