Use builtin Flask dev server for development
Update existing templates to HTML5

Also utilize templating better and add some weak CSS
Organize imports and clean trailing whitespace
Clean up /emails/
Clean up GET /
Add send_email function, but it's not implemented

Waiting on philipdexter/pyboard#9
Reference philipdexter/pyboard#4
Add error page and fix the "nopes" everywhere
Add template for /grades
Add some page titles, FIXMEs, and aborts