[10970] Implement mass mail send infrastructure.

It expected to be used in 2 case: some gameevent must send mails at start/end,
and this can be useful in game commands. Both case wil implemented in later commits.

* New MassMailMgr can accept tasks for send mass mails in safe way for map update threads context/etc.
* It work in way:
   - By provided race mask or more generic SQL query string in async query selected affected characters
   - At query result ready at next world tick update in safe common part of tick code some from mails
     from queued mas mail tasks send.
   - Amount mails limited MassMailer.SendPerTick confir option (10 by default). This done for prevent
     high server load/lags at send too many mails in one tick (mail send all existed characters in DB
     who match to seelction criteria)
   - Manager not persistant for server shutdowns so any not send mails in queue lost at shutdown.
     But with default setting 10K mail send in 20 secs (10000/50/10). Adding more safe execution
     for this case will make related code lot more slow and req. many DB tables and code support.

src/game/World.cpp

@@ -42,6 +42,7 @@
 #include "SpellMgr.h"
 #include "Chat.h"
 #include "DBCStores.h"
+#include "MassMailMgr.h"
 #include "LootMgr.h"
 #include "ItemEnchantmentMgr.h"
 #include "MapManager.h"
@@ -618,6 +619,8 @@ void World::LoadConfigSettings(bool reload)
 
     setConfig(CONFIG_UINT32_MAIL_DELIVERY_DELAY, "MailDeliveryDelay", HOUR);
 
+    setConfigMin(CONFIG_UINT32_MASS_MAILER_SEND_PER_TICK, "MassMailer.SendPerTick", 10, 1);
+
     setConfigPos(CONFIG_UINT32_UPTIME_UPDATE, "UpdateUptimeInterval", 10);
     if (reload)
     {
@@ -1404,6 +1407,9 @@ void World::Update(uint32 diff)
     ///- Update the game time and check for shutdown time
     _UpdateGameTime();
 
+    ///-Update mass mailer tasks if any
+    sMassMailMgr.Update();
+
     /// Handle daily quests reset time
     if (m_gameTime > m_NextDailyQuestReset)
         ResetDailyQuests();