[FAB-2243] Replace Tx Validation bit-array by flags

https://jira.hyperledger.org/browse/FAB-2243



Switch valid flag from a boolean to an enum, so that we can indicate the reason
for the invalidation (txid already exists, vscc validation failure
(endorsement policy failure), mvcc validation failure, etc)

This change adds invalidation reason codes, sets them in the block as a uint8
(byte) array, and returns validation result in GetTransactionById.

Change-Id: I3593bf6aa4f35bb01b14f8fb3d9950b405f84660
Signed-off-by: Ruslan Kryukov <ruslan.kryukov@ru.ibm.com>