Add ability to keep MAC capabilities received via DeviceAnnounce

[mikomarrache]

This change should not impact existing code.

It only consists of adding a new property at the ZigBeeNode level so that one can store MAC capabilities independently of the NodeDescriptor. In our case, we would like to save the MAC capabilities received in the DeviceAnnounce.

The various isXXXXXX methods that depend on MAC capabilities will continue to behave as before the change, since the macCapabilities property will always be null for existing client code.

I also added a method (isReceiverOnWhenIdle).