BigBuckSensingNode: Added documentation to header file

Added description of module at the top, as well as comments for variables
and functions.
BigBuckSensingNode: Finished porting of Wifi on/off code

Ported the turn on/off wifi code from the wifi experiments folder.
Added additional while loops to be robust in case the other system
calls decided to not work. Added a max number of tries to retry.
experiments: back-ported current versions of BigBuckSensingNode wifi

I moved code from BigBuckSensingNode into experiments, to facilitate the
testing of those changes in isolation.