BLK-145 Add 'update' flag to Queue so that a non-unique incoming signal ...

...can *replace* the existing one in the queue

Signed-off-by: Oren Leiman <oleiman@neutral.io>
I agree that this is the way the block properties should look, but it's not backwards compatible. Until we are committed to using block versions and having update scripts that go along with them, I think this needs to go back to how it was.