Corda v4 - Githubissues

This pull request bumps up version of Corda to 4. Changes in particular:

Bumped up version of Corda to 4
Refactored all tests to conform with the new API
Replaced listeners with flow overrides where appropriate
Removed a facility to extend from membership contract class in BNMS as it doesn't work in Corda 4 anymore
Added @BelongsToContract to all states
Made all flows versioned and upgraded them to use new finality apis
Moved to JPA instead of raw DB access

corda / corda-solutions