Working CopyHTML shortcut

closes #3481
- Pressing Ctrl/CMD+Shift+C in the editor will open up a modal that
contains the generated HTML for either the selected text or the whole
post
all the variables in this function are instantiated every time it's called -- you're always going to get `undefined` for all your checks here :/ You can move things to a more global scope, but I don't think it's too harsh to have to do the lookups every time.