This is a terrible hack

In the interest of time, we originally imported the canvas-lms/ui/shared/rce/FileBrowser by dot-doting our way out of the canvas-rce package. While it worked, it also prevented canvas-rce from being used outside of canvas.

Welcome to hack 2, where FileBrowser.js and its dependencies are copied into this package to make us self-contained again.

This must be redone, but solves an immediate problem.