Removed circuit editor setup code that had always been in codemirror-compressed.js

Previously, every page that included codemirror-compressed.js (such as every courseware page) was running code to create a modal dialog for the circuit editor. I've moved those functions to `schematicinput.html` where they belong. 

I tried the editor, and it works (including the modal dialog), but I don't know how to verify it completely because I don't know how to edit circuits...

@cahrens @sarina