Add lightweight model declaration

provide model for DataProcessorDescription [1] and relevant sub-classes,

• OutputStrategy [2] (Determine how event schema looks like)**
• StaticProperty [3] (User configuration in UI, provided configuration input),
• SpDataStream [4] (Stream requirements),
• EventGrounding [5] (TransportProtocol, i.e., used message broker and configuration etc)

We need to provide the necessary base classes Unnamed-/Named-/AbstractStreamPipesEntity.

[1] https://github.com/apache/incubator-streampipes/blob/1827945aefdc8acec68387b447ab1732e0c05543/streampipes-model/src/main/java/org/apache/streampipes/model/graph/DataProcessorDescription.java

[2] https://github.com/apache/incubator-streampipes/blob/1827945aefdc8acec68387b447ab1732e0c05543/streampipes-model/src/main/java/org/apache/streampipes/model/output/OutputStrategy.java

[3] https://github.com/apache/incubator-streampipes/blob/1827945aefdc8acec68387b447ab1732e0c05543/streampipes-model/src/main/java/org/apache/streampipes/model/staticproperty/StaticProperty.java 

[4]https://github.com/apache/incubator-streampipes/blob/1827945aefdc8acec68387b447ab1732e0c05543/streampipes-model/src/main/java/org/apache/streampipes/model/SpDataStream.java 

[5] https://github.com/apache/incubator-streampipes/blob/1827945aefdc8acec68387b447ab1732e0c05543/streampipes-model/src/main/java/org/apache/streampipes/model/grounding/EventGrounding.java