Add moving background.
Merge branch 'master' of github.com:GoogleDH/Contra

Conflicts:
	web/source/Player.dart
	web/source/Statics.dart
	web/source/WorldMap.dart
Merge branch 'master' of github.com:GoogleDH/Contra

Conflicts:
	web/source/Game.dart
Update robot.
Merge branch 'master' of github.com:GoogleDH/Contra