Core/Units:

- Implement UNIT_FIELD_HOVERHEIGHT (requires DB data). This field, sent in update object packet, will determine the height at which a creature hovers if it has movementflag_hover applied. Note that hovering will now update the server-sided z-coordinate by the value of this field, and that all subsequent positional updates to the client will need to send z coordinate MINUS the hover height offset, or the hoverheight will be visually doubled client side.
- Correct our usage of movementflag_flying, movementflag_can_fly, movementflag_hover and movementflag_disable_gravity (previously levitate), and how they relate to InhabitType in the database. This fixes "flying creatures on steroids" bug (wings flapping too fast), and potentially a lot of visual issues in AI scripts. Note that a lot of scripts still set wrong movementflags, these need to be fixed on a case by case basis.
- Send correct packets for SPELL_AURA_FEATHER_FALL, SPELL_AURA_WATER_WALK and SPELL_AURA_HOVER apply/unapply.
- Send correct packet contents for movement update in Unit::SetSpeed.
- Misc. cleanup in affected scripts.

src/server/scripts/Outland/CoilfangReservoir/SerpentShrine/boss_lady_vashj.cpp

@@ -731,7 +731,7 @@ public:
 
         void Reset()
         {
-            me->SetLevitate(true);
+            me->SetDisableGravity(true);
             me->setFaction(14);
             MovementTimer = 0;
             ToxicSporeTimer = 5000;

src/server/scripts/Outland/CoilfangReservoir/SerpentShrine/boss_lurker_below.cpp

@@ -109,7 +109,7 @@ public:
         }
         void Reset()
         {
-            me->AddUnitMovementFlag(MOVEMENTFLAG_SWIMMING | MOVEMENTFLAG_LEVITATING);
+            me->AddUnitMovementFlag(MOVEMENTFLAG_SWIMMING | MOVEMENTFLAG_DISABLE_GRAVITY);
             SpoutAnimTimer = 1000;
             RotTimer = 0;
             WaterboltTimer = 15000; // give time to get in range when fight starts

src/server/scripts/Outland/CoilfangReservoir/SerpentShrine/instance_serpent_shrine.cpp

@@ -153,7 +153,7 @@ class instance_serpent_shrine : public InstanceMapScript
                                         if (Creature* frenzy = player->SummonCreature(MOB_COILFANG_FRENZY, player->GetPositionX(), player->GetPositionY(), player->GetPositionZ(), player->GetOrientation(), TEMPSUMMON_TIMED_DESPAWN_OUT_OF_COMBAT, 2000))
                                         {
                                             frenzy->Attack(player, false);
-                                            frenzy->AddUnitMovementFlag(MOVEMENTFLAG_SWIMMING | MOVEMENTFLAG_LEVITATING);
+                                            frenzy->AddUnitMovementFlag(MOVEMENTFLAG_SWIMMING | MOVEMENTFLAG_DISABLE_GRAVITY);
                                         }
                                         DoSpawnFrenzy = false;
                                     }