WIP: Add client-side graphing code

[dkirker]

• Add option (http_plot_type) to use client side (raw), server side (image), or both (raw,image), graphing
• Add option (http_plot_buffer_size) to define a buffer size for server side graphing (in the event that the server is to update the graph in sub-second intervals)
  • probably remove this

This is just some code that I whipped up. Maybe a good PoC? Fell free to use what you'd like. I think I'll probably remove the http_plot_buffer_size option. I also tweaked a few things, maybe incorrectly, to better support the http terminal for nbfm usage of multi_rx.

[dkirker]

I totally did not see the directory op25/op25/gr-op25_repeater/www/op25-new-ui/ in the new-gui branch. So, this is probably worth closing, but useful if someone wants to use the graph with the old UI.

[boatbod]

When I get some time I'll take a look. Separate from new-gui, I would like to get client side graphing working and already have some hooks in place to send the raw data to the client terminal via json.