Fixed back/menu button behavior

A pressed back/menu button will only be handled once, i.e. when the button is released as opposed to being handled every frame it is held. Added character sprites to sprites pack. Renamed net.pjtb.celdroids.client.CanvasComponent to net.pjtb.celdroids.client.ViewComponent. Some small whitespace corrections. Updated README.md to have more specific clone instructions and have jdk1.6.0_45 in place of jdk1.6.0_43.