Frontend package

The frontend CoCalc application, which is loaded in the user's web browser.

This code is part of https://github.com/sagemathinc/cocalc and isn't currently designed to be used standalone.

Most of the code here should be moved to a subdirectory called src/. There's
also a dist/ directory (not in Git) where autogenerated code gets built. That
code gets used by other packages, e.g., @cocalc/next, @cocalc/project.