set(settings, loadedTheme, checkedTheme) {
        currentActiveTheme = new ActiveTheme(settings, loadedTheme, checkedTheme);
        return currentActiveTheme;
    }
Set theme

At this point we trust that the theme has been validated.
Any handling for invalid themes should happen before we get here

@param {object} settings
@param {string} settings.locale - the active locale for i18n
@param {object} loadedTheme - the loaded theme object from the theme list
@param {object} checkedTheme - the result of gscan.format for the theme we're activating
@return {ActiveTheme}