4x4" Modified Magnetic Openlock/Openforge Base

I modified the original 4x4" base from devonjones ([link](https://www.thingiverse.com/thing:2740279)). It now accepts 4 2x2" tiles and adds stability in the center.

It was made because I resin cast the tiles, and I didn't want to make a separate mould for 4x4 tiles.