Player markers in multiple dimensions

[hrmorley34]

This is an edit to render player markers in every dimension; it also fixes an issue where switching to another map/dimension and then back to the overworld causes all markers to disappear.

It does add markers to every map of a given dimension, so that would include underground/aquatic maps as overworld maps with overworld player markers; this could be changed.

[StrikerTheHedgefox]

Hope this one makes it in. Could really make use of this.