Medium and mobility behaviour insertion for Wmediumd

Hi,

As discussed with Javier Cardona and Javier Lopez this pull request has:
- Code committed following the development process and with comments.
- Global vars reduced to one struct. 
- Folder /wmediumd/tests/test-002-probabilities-with-mobility has scripts and diagrams for testing the code.

Attached diagram shows the app flow using the mobility behavior.

Sorry if there are mistakes :( 

Best regards.

![uml_activity_diagram_extension](https://f.cloud.github.com/assets/4155204/1696948/505af7b4-5ece-11e3-81de-7b7c5cf3ea4a.png)