Add legend open/close state to URL query

[jameshadfield]

Will be very beneficial to iframe embedding and narratives

[emmahodcroft]

@jameshadfield you are a mindreader, I had a rant about this just the other day and it's on my 'auspice wish list' door, but I never got around to making an issue 😆

[jameshadfield]

The best example to follow for this would be to follow how we currently store the state for being able to control the sidebar open/closed state via the URL query (see https://github.com/nextstrain/auspice/search?q=sidebarOpen&unscoped_q=sidebarOpen). Please note that it's not applicable for this to be set via the dataset JSON.

The default state for the legend open/closed should be set as it currently is, and any user-interaction will result in a URL query (via the redux middleware). For instance ?legend=open or ?legend=closed.

[ncallaway]

I'm starting work on this now, I expect I'll be able to have a PR for you shortly.

[ncallaway]

@jameshadfield I've implemented the setting loading side of this (that is, you can add the ?legend=open and ?legend=closed query params to define the default state of the legend.

Do you also want the legend state to persist to the URL query (e.g. the way the c param is updated in the URL to stay consistent with your selection in the Color By dropdown? Or is this more a feature for iframes and embeds, and we shouldn't touch this URL parameter once the page is loaded (the same way that sidebarOpen behaves)?

[jameshadfield]

Closed by #923