Update main.cpp doe to changes in Application.
Improve Neighbourhood constructor, so now it fully sets up UdpMilticastSocket and TimerDescriptor.
Distinguish between Buffer::reset() with and without parameter (one without parameter sets buffer to null).
Fix InputOutputBuffer interface and add InputOutputBuffers::access_input_buffer().
Move readable/writable callbacks from Descriptor to higher classes and introduce Descriptor::write() and Descriptor::read() virtual methods.
Update TimerDescriptor due to changes in Descriptor.
Update UdpMulticastSocket due to changes in Descriptor and also implement UdpMulticastSocket::write() and UdpMulticastSocket::read().