Allow configuring if a message without a message type is editable, resubmittable

[alechenninger]

In #163 we defaulted these to false but IMO null should effectively be a valid entry among types of messages which are editable, etc.

[alechenninger]

Use case: my message was mostly good but for one reason or another consumer was not able to determine its message type so it is sent to EMA. I want to be able to edit the message, fix the issue that prevented consumer from being able to determine message type, and resubmit.

[macgregor]

Yeah, I honestly wasnt sure what to default it to. I dont entirely understand the reasoning behind allowing edit/resubmit for some messages and not other so i defaulted to the safe option. Easy enough to change.