Implement mouse handler in piechart

* **I'm submitting a ...**
  - [x] feature request


* **What is the current behavior?**
The mouse handling is very basic and produces sometimes an unexpected result.


* **What is the expected behavior?**
Mouse behavior to be managed as in workflow builder (with a mouseHandler class).
Expected features : 
  - Change style of parts on mouse over
  - Change color of parts on mouse click


