Created asteroid field level

Need to test for performance issues before pushing to the main branch,
since the level currently has 1728 asteroids. Works fine on my desktop,
although load times are noticeable.
Merge remote-tracking branch 'origin/master' into level-design
Fix Skybox rendering in this branch
Throttle and Keyboard Control Tweaks

Movement didn't feel fast enough in this level, so I bumped up the max
throttle speed and yaw speed. I made the throttle values change faster
so players could get up to max throttle about as quickly as before. I
also slowed down rolling a bit since it felt too twitchy.
More Control Changes

Swapped pitch and throttle on the controller and inverted pitch
controls. Made some keyboard control tweaks so they would be a closer
match for the controller.
Merge branch 'level-design'
Merged level-design with master, and changed controls back.