[Cooja] VariableWatcher 2.0

Now that the memory patch was accepted, here is a first component that benefits from the new abilities.
It's truely not perfect but should be a nice extension to its previous version.

Some of the key features:

- Search in variable lists
- get address and size information of known variables
- read and write data
- live monitoring of memory regions
- freely selectable memory regions
- different display options and line break

![cooja-varwatcher](https://cloud.githubusercontent.com/assets/1416326/4079187/b59a2012-2ed2-11e4-8c6f-f93e162df040.png)