Flesh out a home page

[brandon-patterson]

The main activity should likely act as a dashboard for the different app functions. Set up the basic navigation, and hook each item up to empty pages for now. (Open a new issue for each empty page for adding the detail.)

Potential functionalities (in no particular order):

• Unit analysis/conversion
• Models (gas laws, calorimetry, dilution, titration, etc.)
• Balance chemical equations
• Calculate molar mass/do stoichiometry
• Lewis dot diagrams (best guess at structure, maybe a sandbox?)
• References (periodic table, diatomic elements, common polyatomic ions, etc.)

Lots more could be lifted from the common core curriculum. I imagine we start with the fun/useful/interesting/challenging bits first.