Editor UI is hard to use, feature lacking

[ahirschberg]

The following should be implemented in the code editor to make it more usable:

• apply an action to a region for all steps or multiple steps
• remove a region's action from all steps or multiple steps
• regions should be able to change bounds without deleting and re-adding
• multi-line regions should be drawn more cleanly on the editor to reduce clutter
• region overlap shouldn't get in the way of selecting a certain region
• editor should give more robust options for saving the lesson files
• adding or removing code should update the region bounds - this is an issue with ace.js 😢