Added sourcePreset and warmPresets to the AssetContainer class.
Updated fillFromModel() method in AssetContainer class to include new settings from model object passed as parameter.
Updated toModel() method in AssetContainer class so that it includes all of the current container's properties when creating a Model instance for saving into database table 'asset_containers'. This is done by calling $this->sourcePreset(), etc., which will return null if not set, or whatever value was previously assigned via ->setSourcePreset().
This PR adds the ability to save image presets in the Asset Container settings.