Mission briefings are now working

Mission briefings now appear before every level.  Map names, and their
briefing text are defined in Game.js using the gamestat field of the
Game object.

Breifing screens now clear the viewport to a background color to remove
what was previously on the screen before drawing text.

Text is now correctly centered in breifing screens
Implemented debriefing screens and fixed HUD overlap

I added a debriefing screen and modified the control flow so it goes
briefing, map, debriefing, then increments the level index, then
repeats.

After a level is over, the current HUD is disabled so that it does not
appear during the briefings.
Added persistent score tracking via me.gamestat

#33
#31 When a player dies, the level failed screen is now loaded
#35 adding asteroid sprite, creating map3 with Tiled Map Editor and placing asteroids manually
resources and levels now loaded by xml file
briefings are now defined in the levels.json file
placing level 3 in its correct place
updating map1 and map2 to be smaller and have few enemies
update map size and enemy locations
#35 when a player collids with an asteroid, they lose one health and the asteroid is destroyed
#32 set global maxLevel and now the debriefing screen will go to game over instead of an invalide briefing
cleaning white space
updating map3
#36 changing ship style health to health bar. can define max health and step decrease
gameover screen now shows score from gamestat
the asteroids now spin and each one is scalled 0 and 1.25. Also the direction of velocity is random

The direction is tilted to the positive
clicking menu then play starts the player at level 1 again
re-enabling socket movements
clean up