Change the initial background colour.

It looks cooler in grey.
Fix focus issues with the controls.
Trying to add Pointer Lock support to ludum.js

Doesn't seem to be working yet though...
Add a 'dead' state and try to lock the pointer

- Added a dead state.
- Your health now deteriorates at 1 point per second. When it runs out, you die.
- When you die we go to the 'dead' state.
- After 5 seconds of death, we automatically restart.

You can fire your gun now too - which is to say, if you press the left mouse
button it will decrement your ammo, but that's all.

Trying to use the pointer lock API now too, via the newly-added support in
ludum.js. Not working yet though, unfortunately.