Exception handling

• Throw 400 instead of 500 on invalid JSONRPC structure

Fix empty exception message

Put exception message into the exception container

Some loggers like gelf do not like empty messages

1.1.1

Do not output JsonRpcError data until debug is enabled (#5)

1.1: Exception conversion (#4)

* Revert 2.7 dropped testing

* Exception conversion

* Revert 2.7 dropped testing