Refer-A-Friend System prepared for s1980 adopted from archiv s1699

This is a (nearly) 1:1 copy of the Refer-A-Friend System of the archiv repository at https://github.com/mangos-one/server-old

Taken from
- https://github.com/mangos-one/server-old/commit/00cb8bb4fa9c90e19f612a28f18ad41887f97ee4
- https://github.com/mangos-one/server-old/commit/6a37d17f757075739ec901e222e96fb65bbd6adb

Signed-off-by: Salja <salja2012@hotmail.de>