Figure out a cleaner way to bring in the CodeMirror dependency files

[bmwalters]

Currently we're using bower with several URLs pointing to cdnjs distributions of minified CodeMirror.

This sucks because each resource has its own folder in bower_components, we are required to change the version number in each link when we want to upgrade, and it creates a reliance on cdnjs. Additionally, devs are required to have bower installed to get the dependencies instead of just npm/yarn.

The issue is that minified builds of CodeMirror aren't provided in the npm package.