Play Store production update

This is the last planned postjam2 update. With these changes, the Play Store version has graduated from testing to production!

• Gameplay buttons on Android now anchor to the screen edges.
• Added an options screen on Android. You can toggle music/sound and change which side the Change button is on.
• Added a moment of invincibility when you beat a boss in case it fails to clear all the bullets.
• On winning, the game finishes tallying your final score before letting you return to the main menu.
• Added a freeze on Game Over. This protects against issues where the stage would continue to progress incorrectly.
• Added some UI and pause sound effects.