Enhanced startup performance

Enhanced startup performance due to creation of a separate contextConfig for the shogun-servlet (shogun-config.xml). the core config
(app-config.xml) wont be used as the core and servlet-config anymore.
This way the hibernate-schema-handling will only be executed once and
not twice. This noticeable enhances the startup time when e.g. using
hibernate.hbm2ddl.auto=create