style
preserve_messages no longer mutable
otr_fingerprints no longer mutable
active_sessions no longer mutable
message_history immutable
fixes
style new otr api
centralize this user message handline a bit more
minor
reduce replace access
less replace
smash all the state!
notify slightly lazier
wording
refactor
refactor
minor
Added invalid utf8 check for incoming msgs

Conflicts:
	src/xmpp_callbacks.ml
fixes
require zed for xmpp_client