Modified classes "Receiver" and "RoomMap". Added additional fields and
getters/setters where needed.
Implemented adding/removing receivers from/to map (hard coded, without
offsets)
Fixed a bug in method 'scaleImageToFitContainer' of 'Utilities' class.
Added method 'getScalingRatioToFitContainer'.
Added class 'CoordinateZeroView' which will be a visual representation
of (0,0) coordinate point on the map.
Added 'ReceiverButton' and 'ReceiverButtonState' classes and their image
icons.