Enhanced help section

[clpetersonucf]

Addresses #1505

• Slight rework to content in the main the help page; adds two additional help sections accessible via built-in navigation, for students and instructors respectively
• Student and Instructor help pages address frequent issues & questions related to various aspects of Materia, playing and authoring widgets, scores, and widget ownership

!! Note: these are the default help docs, which do not include UCF-specific support info. Once this PR is merged the Materia-Theme-UCF repo will need to be updated to match.

[cayb0rg]

Well organized, and hits the most common issues. Only thing I see that might need changing is upping the font-size for <dt> tags to 14px or so. Otherwise, I think this looks good to go.