Implement Precompiled Headers (#591)

When applied, this will speed up compile times dramatically.

dGame/dMission/Mission.h

@@ -1,5 +1,8 @@
 #pragma once
 
+#ifndef MISSION_H
+#define MISSION_H
+
 #include <vector>
 #include <string>
 
@@ -259,3 +262,5 @@ private:
      */
 	std::vector<MissionTask*> m_Tasks;
 };
+
+#endif

dGame/dMission/MissionLockState.h

@@ -1,8 +1,13 @@
 #pragma once
 
+#ifndef MISSIONLOCKSTATE_H
+#define MISSIONLOCKSTATE_H
+
 enum class MissionLockState : int
 {
 	MISSION_LOCK_LOCKED,
 	MISSION_LOCK_NEW,
 	MISSION_LOCK_UNLOCKED,
 };
+
+#endif

dGame/dMission/MissionTask.h

@@ -1,5 +1,8 @@
 #pragma once
 
+#ifndef MISSIONTASK_H
+#define MISSIONTASK_H
+
 #include "CDMissionTasksTable.h"
 #include "MissionTaskType.h"
 #include "dCommonVars.h"
@@ -180,3 +183,5 @@ private:
      */
 	void CheckCompletion() const;
 };
+
+#endif 

dGame/dMission/MissionTaskType.h

@@ -1,5 +1,8 @@
 #pragma once
 
+#ifndef MISSIONTASKTYPE_H
+#define MISSIONTASKTYPE_H
+
 //! An enum for mission task types
 enum class MissionTaskType : int {
     MISSION_TASK_TYPE_UNKNOWN = -1,                     //!< The task type is unknown
@@ -24,3 +27,5 @@ enum class MissionTaskType : int {
     MISSION_TASK_TYPE_PLACE_MODEL = 25,                //!< A task for picking up a model
     MISSION_TASK_TYPE_VISIT_PROPERTY = 30               //!< A task for visiting a property
 };
+
+#endif