Reach WebSocket + ProtoBuf based protocol, version 0

Initialisation messages Init and InitAuthenticatedSession both communicate the desired protocol version for the respective session
- Init is a request for all the information necessary to receive and send messages
- InitAuthenticatedSession indicates desire to establish a session allowing for operations specific to reachable peers and attestants.
All responses, including generic Ok/Error ones are represented by the wire::Response enum
- Ok can be assumed to be the default response type when no other response type is specified below
- Unsupported is the response if the node does not support the requested protocol version during initialisation
- Decode Error is the response if any supplied data could not be successfully decoded, including Protocol Buffer Message conversion errors
- Verification Error may be a response to requests with signatures of which the verification failed
- Not Found may be a reply to requests involving IDs that do not identify any information currently stored on the node. All IDed requests are marked as such in the table below

request	user role	response	IDed	description
`wire::Init`		`reach::Reach`		EnvelopeIdHint hint polls, pre-MessageVault upload
`wire::InitAuthenticatedSession`		`reach::AuthenticationChallenge`		request an authenticated session
`envelope::EnvelopeId`		`envelope::Envelope`	Yes	download Envelope
`message_vault::MessageVaultId`		`message_vault::MessageVault`	Yes	download MessageVault
`message_vault::AddMessageVault`		`message_vault::SealedMessageVaultId`		add/upload MessageVault
`envelope::EnvelopeSeed`		`envelope::SealedEnvelopeId`		add/upload Envelope
`envelope::RemoveEnvelopeIdHint`			Yes	remove EnvelopeIdHint by `Envelope.id` and removal token
`reach::AuthenticationAssurance`	Reachable, Attestant			proof of signing ability for authenticated session
`wire::ListEnvelopeIds`	Reachable	`envelope::EnvelopeIds`		lists all EnvelopeIds currently stored on this node
`reach::ReachablePublicKeyRing`	Reachable			add ReachablePublicKeys for a reachable peer
`reach::RemoveReachablePublicKeys`	Reachable		Yes	remove ReachablePublicKeys for a reachable peer
`hint::AddSharedPublicKeys`	Attestant			TODO
`reach::AddReachableVerifyingKeys`	Attestant			add/onboard new ReachableVerifyingKeys
`reach::RemoveReachableVerifyingKeys`	Attestant		Yes	remove/offboard ReachableVerifyingKeys

Protocol processing state change

State changes indicated by "→". If no state changes are indicated, as well as in case of failures (Unsupported, Verification Error etc.) state remains unchanged after processing the request.

Init:
- reach::Init → Ready
- reach::InitAuthenticatedSession → Pending Authentication
Ready:
- envelope::EnvelopeId
- message_vault::MessageVault → Pending Envelope Upload
- envelope::RemoveEnvelopeIdHint
Pending Envelope Upload
- message::AddEnvelope
Pending Authentication:
- reach::AuthenticationAssurance → Authenticated (Attestant) | Authenticated (Reachable) | Ready (Error)
Authenticated (Attestant):
- hint::AddSharedPublicKeys
- reach::AddVerifyingKeys
- reach::RemoveVerifyingKeys
Authenticated (Reachable):
- wire::Request::ListEnvelopeIds
- reach::AddReachablePublicKeys
- reach::RemoveReachablePublicKeys