#180 created SlidableWMSServiceLayerGroupInternalFrame. Moved GUI parts from SlidableWMSServiceLayerGroup to that class
#180 after the layer is removed, remove the retrieval listeners on the several child layers
#180 comments
#180 add and remove the timer listener
#180 if a internalframe is removed from the mappingComponent, it has to be first disposed and afterwards it has to be remved
Merge branch 'bug/180-memory-leak-SlidableWMSServiceLayerGroup' into dev