Messages in sequence diagrams can have a number to display an order, which can be entered in the select operation dialog. For each message a dedicated number has to be entered. To ease message adding it would be nice to let umbrello auto increment this sequence number. 





Reproducible: Always

Steps to Reproduce:
1. create sequence diagram
2. add message with sequence number 1
3. add additional message
Actual Results:  
You have to enter sequence number 2 by hand. 

Expected Results:  
umbrello should present the next number e.g. 2 without any required user interaction.