It's possible to launch a lot of instance of ktimetracker, but this create problems and the user is not informed that he have more than 1 instance of ktimetracker launched.

Reproducible: Always

Steps to Reproduce:
1. Launch ktimetracker
2. Launch ktimetracker an other time
3. Launch ktimetracker an other time
Actual Results:  
There isn't a message telling you that you have 2 or more instances of ktimetracker. With some desktop environment, it can be difficult to see that you have a lot of ktimetracker opened. If there is too many ktimetracker opened, some problems appear (cannot record timetracking, if there is subtask opened, they will be closed / hiden, maybe wrong data...).

Expected Results:  
It will be great, as for exemple in TimeSlotTracker, that a window appear when you relaunch ktimetracker a second time, telling you : "Sorry, only one instance of Ktimetracker allowed. Press ok to exit".