Core/BattleGrounds: store data about BGs victories

And output with https://github.com/ShinDarth/PvPstats or similar tools ;)

It stores all Battlegrounds:
- date & time
- winner faction (ally, horde or noone)
- type (if WSG, AB, etc..)
- bracket_id (the bracket level range)

For each Battleground it also stores player:

- killing blows
- deaths
- honorable kills
- bonus honor
- score damage done
- misc attributes (like WSG cap/def flags, AB assault/def bases, EoS cap flags, etc...)

Also this feature is disabled by default, can be enabled via config file:

Battleground.StoreStatistics.Enable = 0

thanks @DDuarte and others for helping