initial implementation of JPA persistence binding.
added jpa config values in openhab_default.cfg
fixes to transaction management in jpa persistence service. a new entitymanager is created and closed for each transaction.
only name refactorings.
some modification for a separate configuration class (as in db4o binding. This modularity will help in unit tests.
some refactorings. considering varchar uses 4 byte if empty made me switch to a one entity approach having a simgle value column which can take upto 200k.
minor simplifications.
Merge branch 'master' of https://github.com/mdbergmann/openhab