Rebased "Test serialization of extensions #599" to fix revert #637
Rebased "Test serialization of extensions #599" to fix revert #637

pmconrad/graphene,oxarbitrage/bitshares-core,bitshares/bitshares-2,oxarbitrage/bitshares-core,pmconrad/graphene,bitshares/bitshares-2,oxarbitrage/bitshares-core,bitshares/bitshares-2,bitshares/bitshares-2,pmconrad/graphene,oxarbitrage/bitshares-core,pmconrad/graphene