Checkbox text labels handling large dynamic strings differently

[marlitas]

From #268.

One seems to be limiting based on a maxTextWidth and another seems to be using multiple lines in Rich Text to overflow the large string. This is probably due to the fact that "Reference Line" has a space in the string which allows it to be added onto a new line.

I'm unsure how frequently we would run into this situation, but it seemed visually bizarre enough to create an issue to put eyes on it.

[marlitas]

In the integral, advanced and lab screens I also noticed the grid checkbox icon can collide or completely disappear into the menu bar with longer strings.

[pixelzoom]

TangentLineCheckbox, AreaUnderCurveCheckbox, and ReferenceLineCheckbox are in fact handling their strings identically -- they all use RichText, and allow the client to use whatever markup they want.

If you change "Tangent" to "Tangent<br>Line" in calculus-grapher-strings_en.json, you'll see that it behaves the same as the other checkboxes:

Or change "Reference<br>Line" to "Reference Line", and you'll see:

Using RichText anywhere in a sim does bring up the possibililty that the string height (not just its width) may become problematic. Maybe it's a bad assumption, but we assume that translators tests their work, and would notice a case like #283 (comment). But as a bit of defensive programming, I've added maxHeight to the RichText checkbox labels in the above commits.

Back to @marlitas for review, close if OK.

[marlitas]

Looks much better and feels like a better safe guard. Closing!