Update Installation model class (supporting multiple categories) and the direct category usage
Supporting multiple categories for the SENDER API
Store categories as set; add JPA annotation for collections
Adding MEMBER OF statement
Adding IN ELEMENTS() function for the multiple categories
Adding setEntityManager() hook
First test-case for the InstallationIMPL and its DAO
Adding JPA test resouses
Adding some test dependencies
Some refactoring and adding tests to query PushEndpointURLs