Update components to codemirror 4.7
Merge pull request #6865 from takluyver/cm4.7

Update components to codemirror 4.7
initial take on promises
Initial stab at adding promises to the widget framework.
Fix view rendering order.
Add Promise support to models.
Use load_class in comms instead of callbacks.
Proxy console.error calls
Simplify code by using Promises in a better way; try_load -> load
More simplifications due to promises
Add some error handling for creating views and models
Better error messages with correct stack traces
Dictionary key/value typo
Load the utils module
Fix some this vs. that errors, as well as returning some promises to wait for fulfillment
Make display also pend on set_state.
Add a WrappedError class
Finished adding error handling.
Use rsvp.js for Promises
Bug fixes