[12587] Chat system refactoring All chat function now call same method

I also reworked the packet structure to be more near of original.
Due to havy of code changed this commit need to be applyed carrefully.

Any feedback is welcome here or on cmangos.net
[12588] Restore nix build. Also forget to remove one MANGOSASSERT + cosmetic stuff
[12589] New nix fix, sorry.

Enum place swap and a new include.
[12590] Add BuildChatPacket comment, reorder parameters, correct a little bug gm name not showed on general channel (Thank to @Shauren for pointing).
Merge branch 'master' of https://github.com/cmangos/mangos-wotlk