Add endian awareness to the protocol

[Zepheus]

Right now, most of the message serialization uses memcpy directly to construct the over-the-wire payload.

Whenever these structures include integers, they are implicitly encoded in the machine's endianness. This will cause a binary incompatibility on machines that do not provide flexible endianness per process (e.g. MIPS?)

We should abstract this away using helper functions from the htons, htonl, ntohs, ntohl family.
Alternatively, we could use flatbuffers and gate this under protocol negotiations. This would greatly speed up adding message types in the future.

[AhmedSoliman]

We discussed that and we don't think this is something we should be doing at the moment, it's a big change with little value. I will close this for now, but we can re-visit this in the future.