[Cooja] Simple mote tooltip for Visualizer

When working with different mote types that run different programs I've found it sometime laborious finding out which mote in the Visualizer runs which type / which software.
Therefore I've added a simple tooltip that displays for each mote the mote type name and the executable / sourcefile it executes.

![visualizer-tooltip](https://cloud.githubusercontent.com/assets/1416326/3839948/42a07186-1e17-11e4-9c5a-9e819100a8ff.png)