Expose more panel toggles through APIs

[lmeyerov]

It's unclear, via APIs, how to toggle, especially during load-time, the various panels: timebar (+ choice of dimension?), histograms, table inspector (+ choice of nodes/edges/events?), legend (+ choice of tab?)

I'm thinking:

• url exposed, and documented in nexus
• js exposed, both vanilla + react, and documented in storybooks
• pygraphistry deferring to url param ok
• maybe defer parameterization for a later day?

[lmeyerov]

To scope down until something richer needed, maybe start with just url api?