fix single mode
Revise game tutorial text
Format JS
Add sceneAddCmd to character
Add world scene remove Cmd, add skeleton Sprite inheritance
Add sprite base class for all unit visual representations, provides hooks to add and remove self from scene. Convert bar classes to use Sprite base class
Refactor bars to use Sprite removeSelf hook, also refactor character initialization
Remove barAspectRatio as class var of character
Added SpriteFactory to initialize all sprites (robots, health bars, almost anything displayed on screen that needs to be updated)

Format Bullet.js
Added add sprite cmd and remove sprite cmd, which both work - used for post-init and pre-destroy behavior
Modify sceneAddCmd, sceneRemoveCmd to more general setup and destroy hooks
Convert new Array to preferred []
Update Bullet to use Sprite

Keep characters in sync between Grid and SpriteFactory
Remove references to bullets in Grid.js, replace with accessor method of getBullets from spriteFactory
Updated destroy() of bullet to use active to indicate that it needs to be removed from the container that gets called for updates
Add general purpose updateContainer for removing inactive sprites from the scene and updating the containers of SpriteFactory
Add getBullets forwarding method in Grid.js to prevent desyncing of bullet container
Fix use of alive to active when referring to Character