renamed *RadioMediumObserver to *Observer
renamed/refactored  add/delete RadioMediumObserver to add/delete Observer for equivalency with other parts of the project
concurrency fix set/get BaseRssi
Fixed the concurrency of the WeakHashMap used by setBaseRssi and getBaseRssi and running the updateSignalStrengths in a Simulation Thread because of concurrency
start DGRM plugin with cooja_default.config
start the DGRMconfigurator within the cooja_default.config instead of starting in DirectedGraphMedium.java
BaseRSSI plugin added
plugin to view and change the base rssi.
for further implementation of random base rssi generation
deleted unneeded if
can never be null
start DGRMVisualizerSkin in cooja_default.config now
instead of starting in DirectedGraphMedium