flexible datatype plotter widgets

[guruofquality]

• remove dtype from constructor and available params
• accept incoming buffers from streams and packet messages
• accept dtype from the incoming buffer

[guruofquality]

https://github.com/pothosware/pothos/commit/f034e67f9bd3a6d1b5b172307eb0cbcfefc12ddc

• OK - remove dtype from constructor and available params
• OK - accept dtype from the incoming buffer
• TODO - accept incoming buffers from packet messages

[guruofquality]

Snooper now forwards messages, the wave plotter can already deal with packet messages of arbitrary sizes: https://github.com/pothosware/pothos/commit/096b4c8754c1974075857aa4928e521532bf323a