Rollback addons structure

ofxXmlSettgings and ofx3dModelLoader libraries files where moved to make them comply with ofxAddonTemplate but that will break a lot of projects. This reverts that commit

ofxXmlSettings will be deprecated by ofXml at some point and ofx3dModelLoader is not so used anymore in favor of ofxAssimpModelLoader so it's ok that they are not updated to the new structure