[Vis] Planning signal plot display for All Channels

Per 18 Oct TechComm meeting,
Display all (e.g. 128) channels is important to explore soon.

To do: investigate modifying current signal plot to display the full montage (e.g. supporting 128 channel) or a feasible subset of channels.
Originally it was decided for this module that this feature should wait until developed as a popout (#71).

Signal plot currently displays 6 or 12 channels well and encounters serious performance issues at 18 channels (piloted during #76)

@andesha to explore feasibility this fall, including benchmarking against browser performance.
with new developer resource, across :

* back-end: protobuf displaying chunks at a lower resolution
* loris-mri: chunking scripts and file system storage
* front-end: cursor text, channel labels, default time range displayed

- Investigate to determine: What would it take to do this currently in the EEG browser - what are our best options?
- Develop a plan/recommendation with time estimates.