Penultimate PR before multi chat completion

Allows a chat to send invite to target peer via API
Allows peer handler to accept the chat invite or reject
Joiner reply auths inviter against invitee with bi-directional handshake and passing of encrypted session key.
Laying the groundwork for the rest of the chat part to acknowledge new member with shared session key.
Added new test test_protobuf.c
Added ability to turn on and off all forms of encryption with -DNOSYMMETRICALCRYPTO and -DNOASYMMETRICALCRYPTO

AlexsJones / whisper-core