Rework Rabble admin to be a React application

[shinyvision]

There's still a lot of scripts requiring jQuery, especially collections in the ContentBundle. It would be ideal if this could be migrated to React.

[shinyvision]

I just changed the title of the issue, because I'm very appealed by the idea of the admin system being a React application. I'm not sure how practical this is, but research can be done.

If this is not practical, then for sure a lot of existing elements will be replaced by React components.