Ground Plunderer printability tweaks

Tweaked niphilim's already-improved models to save you some time:

1) Side-mount turrets now print out in 8 pieces each instead of 16.
2) Removed dead space in "side_right.STL" allowing it to print on a makerbot-sized bed.
3) Added "less overhang" variants that make small compromises to print a little cleaner.

See https://www.thingiverse.com/thing:1429694 for the other pieces not included here.

Thanks to outofstep and niphilim for the actual models.