Fix preset dropdown always defaulting to 'no preset'

[canstudios-nicolaw]

Fixes #2379

In https://github.com/adaptlearning/adapt_authoring/pull/2371/files in plugins/content/config/index.js the following was removed

var configModel = records[0].toObject();
configModel._enabledComponents = uniqueComponentList;
return next(null, [configModel]);

and replaced with

return next(null, [records[0]]);

This missing .toObject led to the following change 33600c3#diff-6cb64d73a547a24bfc001f80bb7192dc

These two things meant that the _themePreset value was no longer being saved. Fixing these things allows the last selected preset to be saved successfully which fixes this issue.

To test
Select a theme
Select a preset
Save
Open theme editing page, theme and preset should be selected
Change theme
Return to original theme, preset should be selected