Childclasses for Entities and Entity specific QueryBuilder

#Childclasses for Entities: 
(see #1 )
To seperate generated code and manually implemented code in the Entities we need a mechanism to enhance entities with manually written code. Usualy in MDD you solve this with child classes. greenDAO should have the possibilty to use child classes for entities.

#Entity specific QueryBuilder
(see #3 )
for easily find entities, it should be possible to generate an Entity specific QueryBuilder which builds predefined Queries like

findByPrimaryKey
findAll
findByExample