ADD: Storage: References

[steffenkux]

Current situation

Storage API only defines references from a message to old messages. It doesn't define any links from the original message to changing messages (EDIT, REPLY, DELETE).

Requirements

A message entry in the chunk contains references to:

• EDIT: It is a reference (hash, chunk) to a message with the edited content. By knowing the message, also the next editing message is known. This might be a list of depended message iterations.
• DELETE: references (hash, chunk) the message which deleted this message
• REPLY: a list (set) of messages which added a reaction

additional info

A deleted message stays in the storage but is marked as deleted. As it can't be enforced to delete a message completely, delete means: "This message was removed from the conversation." Pruning the storage is optional.