Use area_effect_cloud for marker entities instead of armor_stand

[Adrodoc]

This should affect all Minecraft versions, because AreaEffectClouds were introduced in 15w33a and the first supported version is 15w35a.
This is not a patch but at least a minor version change.

[BrainStone]

Mind to explain why they are better?

[Adrodoc]

They have a slightly smaller overall performance impact: https://www.youtube.com/watch?v=RKXzWGQfIcg