Read/write themeVariables from config instead of course

[taylortom]

Summary

As part of moving themeVariables storage from the course record to the config record (to align with framework PR adaptlearning/adapt_framework#3578), the theme editor UI needs to read and save themeVariables on the config model instead of the course model.

Changes needed

In editorThemingView.js:

• initData: Read themeVariables from Origin.editor.data.config instead of Origin.editor.data.course
• postSettingsData: Save themeVariables to Origin.editor.data.config instead of Origin.editor.data.course

Related

• adapt-authoring-coursetheme counterpart issue for backend changes