Feature/spawnattack at enemy

1. Added the ability for SpawnAttacks to let the units spawn when the projectile arrives at the targetpos. 
2. Added a bool spawnAtTarget to spawn attack in which you can define whether the unit spawns at the target or at the attacker.

In Addition i changed the command which is given to the spawned unit to an attack command on the target cell. Unit will always try to attack if it has an attack command.
( I think this makes way more sense than giving a move command to the meeting point)
( This also works if the spawned does not have a attack command. It will move to the enemy then)

so the "new" syntax is ```<unit value="warrior" amount="10" spawnAtTarget="true" />```
if you want to let the unit spawn if the projectile arrives you need to use titi's new projectile syntax and add the unit node to it
Example:
```
			<projectiles>
				<projectile attack-start-time="0.25" damage-percentage="100">
					<particle value="true" path="particle_proj.xml"/>
					<hitsound enabled="false">
						<sound-file path="$COMMONDATAPATH/sounds/archmage_hit.wav"/>
					</hitsound>
					<unit value="warrior" amount="10" spawnAtTarget="true" />
				</projectile>
			</projectiles>
 ```
Ask me if you have any questions