Move persistence mappers into separate application

The persistence mappers which are generated by MyBatis are moved into a
separate enterprise application and are exposed as EJBs. Packaging the
EJBs as an EJB archive does not suffice, because EJB archives are not
supposed to contain dependencies.

MyBatis generates the mapper classes at runtime and there seemed to be
no simple way to expose these classes as directly as EJBs. Therefore,
the mapper classes are exposed through proxy EJBs and the mapper classes
are autowired by MyBatis-Spring.