* adds an RNG argument to the transaction queue
* minimal support of transaction queue RNG in tests
* added the TransactionQueue trait object
* review comments and streamlining of trait bounds
* removed the RNG from the transaction Q and placed it into QueueingHoneyBadger
* formatting fix
This makes Honey Badger a bit more complicated but a lot more flexible:
It is now unaware of transactions and basically just runs one Subset
instance per epoch.
That way, users can use any kind of external queue, control throttling
and prioritization.