Engine: Polymer bugs (and potential fixes?).

Making this issue to keep record of the polymer issues I've found, and potential fixes.

• The depth cutting/fighting on sprites could likely be fixed by setting glDepthMask to false like polymost does when drawing them.

• Depth is something a bit fucked when dealing with transparent/masked ceilings and floors. (Might be related to the glDepthMask change I mentioned, which I'm still messing around with. glDepthMask might also need to be disabled as well when drawing them?)