Revert to normal CodeMirror behaviour when theme is set to "default" or "tiddlywiki"

[grooveboxunited]

Currently when you go to Settings -> CodeMirror -> Set a Theme, and set the theme to anything other than cmplus, much of the features of cmplus remain present, including the text formatting.

I think it would make more sense if switching to these themes disabled all the features of cmplus. Obviously this can be done by disabling the plugin, but this is inconvenient and makes less conceptual sense than just switching the theme.