New features

• Added a new button in the settings to submit bug or feedback reports
• Switched to a more reliable player ID storage
• Adjusted the tutorial to show more info on sludge and gems
• Changed HP bar colors to be different for player and enemy units
• Tower upgrade increases are now shown in the UI
• Added an end game screen upon completing all the levels
• Added more level backgrounds that switch every 10 levels
• Added unit death sound effect