* Completed draft implementation of witness JSON-RPC endpoints for portal network bridge.
* Updated Nimbus RPC configuration to support enabling experimental endpoints.
* Moved witness verification tests.
* Added json test for getProof.
* Added main procs to new tests to fix test suite.
* Added getBlockWitness test to blockchain json test suite.
* Added tests for experimental RPC endpoints and improved the API to support returning state proofs from before or after block execution.
* Correctly rollback transaction in getBlockWitness proc.