More lighting work.

Created by: PJB3005

• Fixes #4869 (closed)
• Makes apply_lum() and remove_lum() go by if a turf ACTUALLY has an overlay instead if it should, because how it was currently implemented didn't take the area's lighting_use_dynamic into account, and at that point there were 3 goddamn checks in those if() statements so I just used what we have, instead of what we should have.
• Also gives shuttle turfs dynamic_lighting = 0, because they really should.
• Fixes #4882 (closed)
• Fixes #4895 (closed)
• More optimizations.
• Fixes some pooling issues.
• Basically reverts #4886, it broke a lot of shit.
• Adds extra logic & math to update_lumcount() to make it only cause updates if it would actually matter.