Up-to-date applet-skeleton

If core-features or the libawn change, the structure of an applet might change as well. Up to now we had some example applets that shipped with Awn, but they are all (a bit) different as of structure. I think we can try to keep the quality of new developed applets high if we supply a skeleton for applets. If we can keep the skeleton up-to-date and show developers how things should be done, we can always point to that skeleton if we decide that a proposed applet doesn't meet the requirements to be integrated in Awn.