added WheelEncoder model

...af3/platform/raspberry/ui/prototype/ProtoypeProvider.java

...ortiss.af3.platform.raspberry/trunk/model/raspberry.ecore

...iss.af3.platform.raspberry/trunk/model/raspberry.genmodel

org.fortiss.af3.platform.raspberry/trunk/plugin.xml

...af3/platform/raspberry/compose/RaspberryPiCompositor.java

...aspberry/generator/executable/WheelEncoderExecutable.java

...berry/generator/transform/WheelEncoderTransformation.java

...platform/raspberry/util/RaspberryModelElementFactory.java