Improvement: Visualisation of Spectrogram on Hydrophone

[bensherlock]

Visualise a spectrogram as for a virtual hydrophone in the water.

[bensherlock]

This can be implemented as per Modem with connection to network socket and receiving AcousticPackets as scheduled by the Controller. AcousticPacket now includes SPL as seen at the node position along with frequency band information. However, this wouldn't allow Hydrophone visualisations in Playback mode, only in Live mode.