Track from box select not present when initializing and re-rendering

[ldr426]

• Specify an echogram with a certain channel to get a box-select area as input for track. But when initializing, it cannot put the echogram and track in the first panel. Need to put them in different panels by order (first echogram, second track). Can be solved by setting the default value.
• Right now, we get rid of the updating button to dynamically update track based on streaming change of the select box. But after re-rendering of the echogram(like using Sv range slider, recalling the echogram function), the track just disconnects with the corresponding echogram, but needs to call the track function again to build connection. I assume the reason comes from the update of dependencies object. Track depends on the corner values of streaming change of the select box. The object(select box) registered for callback is still the old one after echogram re-renders.

From: https://docs.google.com/document/d/1QL89eLLcnLjhV8FRp4L_V1n52z0EbTwrrceGELBhVes/edit

https://github.com/OSOceanAcoustics/echoshader/pull/131

[valentina-s]

@ldr426 Could you provide notes on the solution you are working out regarding unifying the channels (i.e. using the subscriber).

[ldr426]

Has been solved using add_subscriber in Holoviews