Time estimate or Size

medium

Problem

Closes #489

Solution

`ButtonClass`

Rather than passing in a string like "primary-button" that will be handled by something like ButtonClass.Primary.

Bringing NavButton into this new system meant tweaking the css selectors to say "primary-button" instead of just "primary" but styling is not actually changed.

`IconGlyphs`

While I was at it I made the enum IconGlyphs so that using icomoon glyphs doesnt require manually applying several strings in a class name, seemed like a related enough change for this PR.

New feature (non-breaking change which adds functionality)

Steps to Verify:

Everything should look and act the same as before.

Coverage report

St.^{:grey_question:}	Category	Percentage	Covered / Total
🟡	Statements	68.58% (+0.7% 🔼)	657/958
🟡	Branches	65.22% (+1.04% 🔼)	90/138
🔴	Functions	36.21% (+0.84% 🔼)	84/232
🟡	Lines	67.16% (+0.77% 🔼)	589/877

St.^{:grey_question:}

simularium / simularium-website

Feature/button constant #501