I added users, and everything broke :(

The react component part takes too much memory to compile, so i added aggressive code splitting. Now different components (which are ended up as web components) are now independent files and are lazy-loaded. Things like perseus and mathjax are still big files but loaded separately.

I added a top bar and a sign in screen! Also user roles like Admin, Content Manager, Teacher, Student. The sign in screen works!

Also exercises creating, editing.