This CR introduces a custom transaction processor which
can be written and registered with the ledger component.
During commit, if a ledger observes a transaction which is
of not an endorser type (i.e., it's not pre-simulated) and
a custom processor is registered for that type, the ledger
gives a chance to the processor to execute the transaction
and commits the produced output if passes mvcc validation.

At large, this introduces the possibility of deferred transaction
execution.

Change-Id: I525d7b413a131007a1e04dc466f3a2d057b869bb
Signed-off-by: manish <manish.sethi@gmail.com>