Add utility for normalizing vectors.

* Expose earth radius and reduce it.
* Add methods that normalizes the scale of vectors to a specific value.
Merge branch 'develop' of github.com:adam-borzecki/asteroid-defense into feature/miner-missile-interaction

Conflicts:
	asteroid-defense.xcodeproj/project.pbxproj
	asteroid-defense/Application/Projectiles/Nuke.m
	asteroid-defense/Space.m
	asteroid-defense/ViewController.m
Add contacts between nodes.

* Added collisions between earth and asteroid.
* Added collisions between nukes and asteroid.
* Added miner classes.
Initial asteroid spawner, update gravity code
Remove renamed file
Refactored collision logic in Space to a manager.
Fix conflicts
Merge Conflicts
Add Miner collision logic.

* Add projectile interface.
* Refactor nuke launch to projectile launch.
* Implement miner physics and rendering.
Merge branch 'feature/asteroid-generator' of github.com:adam-borzecki/asteroid-defense into feature/miner-missile-interaction
Add launcher buttons on Earth.

* Add miner launcher button.
* Add nuke launcher button.
* Add images for launcher buttons.
* Integrate launcher buttons with Space.
Add miner and asteroid collision.

* Tweak miner stats to only slightly deflect asteroids.
* Add noCategory.
* Implement miner to fade out on collision with asteroid.
Update UI and integrate GameManager.

* Update UI to be more usable.
* Integrate GameManager with the game engine.
* Integrate health with earth, resource accumulation, and armament
accumulation.
* Modify speeds of projectiles to be more easy to use.
* Add new images for UI.
Merge pull request #4 from adam-borzecki/feature/miner-missile-interaction

Feature/miner missile interaction