Dark Mode

[SimonRothUCF]

Adds dark mode styles to the Materia website as well as a toggle on the settings page.

[clpetersonucf]

The visual changes are terrific, and we discussed the issue with duplicate styles in our one-on-one. Here are some minor issues I identified while looking through the site:

Header:

• Materia top-left logo is a PNG. Should be SVG for both, with light and dark strokes (I can provide the original illustrator source file/SVG if needed)
• Support hover links in header are not styled for dark mode (requires your local user to have the support_user role, instructions for doing that here.

My Widgets:

• Excessive box-shadow around My Widgets container in light mode
• instance search input too dark, text is black
• Student Activity -> Individual Scores search input is too dark, text is black
• Share with your Students -> Play URL and Embed Code inputs too light, should be consistent with dark mode inputs
• Settings Dialog -> Attempts slider not styled for dark mode
• Collaborate -> Search input not styled for dark mode
• Copy -> Search input not styled for dark mode

Score Screen:

• Score Screen -> Content area BG Too light. Default table cells BG too dark. Colored correct/incorrect cells too light. Score circle BG text should be light.

Admin panels:

• User and Instance Admin content areas are not styled for dark mode

Widget Pre-embeds:

• Updated pre-embed views (No attempts, not yet available, embedded only) need to be fixed when using dark mode. This one isn't 100% on you, I modified these views in 10.3.0, they'll just need dark mode variants.

Additionally, I committed the style cleanup changes I already made and opened a PR targeting this branch, which is available here: SimonRothUCF#1