Send on channel refactoring

[S-S-X]

Improves event API a bit by making few things bit more uniform.

Changed signature of few event handlers that I think have not been used much outside of beerchat mod.

Moves more stuff away from beerchat core to modular extensions which makes configuration easier.

• Closes #83 Makes beerchat.send_on_channel(...) handle both local and remote chat, basic high level messaging API. Adds beerchat.send_on_local_channel(...) which handles only local (minetest) chat and skips remote platforms.
• Fixes #29 Was using broken events to decide if player is banned, updated registrations.
• Allows implementing #56 Rewriting of channel message parameters added. Leaves few things out like /me message but offers basics for normal messages.
• Fixes #28 Not sure if this is good, it actually might be better if jailed players only receive jail channel messages...

[S-S-X]

I guess then rest of it can be tested in production. I've not done actual play testing but have tested / verified at least part of the logic offline.

This will cause duplication of some messages sent towards bridge but this is expected behavior and fixing it requires removing duplicate calls from other mods. For example this: https://github.com/mt-mods/beowulf/blob/f824064b0f68ed79c5a9f9b2405e7c890aa059f5/df_detect.lua#L232-L235

Should be changed to be like this (or similar but with message table):

        if has_beerchat then
-           beerchat.on_channel_message(beerchat.moderator_channel_name, "DF-Detect", msg)
            beerchat.send_on_channel("DF-Detect", beerchat.moderator_channel_name, msg)
        end