Allow themes to have `config` folders

Description of the need

Currently CMI does not scan themes for a config folder. Not sure if there is any major disadvantage to doing so, but it may be helpful in solving Use config for color module palettes

Themes do save data in config, but only by syncing from the info file during enabling, and/or saving the settings form.

This may also allow deprecating info file settings such as settings[]=xxx etc.

Proposed solution

Allow themes to have config folders