Issue 857 - Chart loading skeleton

[jaronheard]

Resolves #857.

This adds a loading skeleton to charts.

Prior to this PR, charts did not have a height before they were loaded, so it caused a page reflow.

Before	After

That said, there's a number of things on this PR that I'm not especially confident in.

• This adds a dependency on @material-ui/labs, as the Skeleton component is not yet in the @material-ui/core. Rather than add a dependency, should we just implement this as an individual component?
• Should the Skeleton be its own component? Or is it ok to just have it be implemented in ChartWrapper?
• I added a check for safeData to avoid having the charts throw errors if data is null and isLoading is true, but it smells fishy to me.

[ghost]

This should be default! Then it fixes all the problems, maybe... no weird safe data checks!

[jaronheard]

I changed this but unfortunately some kind of weird safeData checks are still required because of the way the components are structured. There's probably another cleaner way to fix this -- after demo day

[ghost]

We should have the isLoading prop in all visualizations so we don't have to do the conditional chart mount which causes a layout jump. If that's done here, I'll update the cards in #873 to use it, otherwise if mine is merged first we'll need to do a sweep later and update them.

[ghost]

Height ratio is off. Also, to keep this user friendly we should show the user something besides just a grayish rectangle. Could be as simple as some words or a loading spinner...

[jaronheard]

Current status for this PR:

• It adds a skeleton with the proper height to ChartContainer.
• It resolves Color names in data result cause issues with VictoryCharts #914

It adds a note about a newly discovered issue with LineChart, which will be covered in another PR:
If there are lines that have different numbers of data points, then they will be colored incorrectly.

[ghost]

Loading "skeleton" ratio now works and has a spinner to indicate somethings happening. Tests and documentation look good for protectData