Core/Movement: Prevent pet animation stuttering during movement (#1142)

* fix vanity pet distance and angle
* fix vanity pet distance to player
* put size calculation for normal pets into the if-statement for vanity pets
* change pet speed algorithm
* change distance calculation
* another change to the distance calculation; differentiate between player running or flying

src/server/game/Entities/Unit/Unit.h

@@ -2561,6 +2561,7 @@ class Unit : public WorldObject
         bool m_duringRemoveFromWorld; // lock made to not add stuff after begining removing from world
 
         uint32 _oldFactionId;           ///< faction before charm
+        bool m_petCatchUp;
 };
 
 namespace Trinity