[12586] Fixed issue with PCH not working on some versions of GCC

Since some versions of GCC doesn't output patchlevel on -dumpversion the PCH check can fail.
Bug: https://github.com/cmangos/issues/issues/81
[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
Nix build fix