Style updates: first pass!

- Removed most explicit widths in favor of filling container
- Added a mixin to remove duplication in font styles
- Consolidated styles in a few places
- Added a touch of branding in the header
- Added basic mobile optimization
- Added some user-specific copy edits
- Moved contents of `application.css` to `globe.scss` to be able to use sweet, sweet SCSS
- Probably other stuff?