Formula Mix-up! Challenge System!

Another new update, this one is a bit more ambitious than my previous ones.
To try to make gameplay more interesting over longer periods of time, I've added Challenges!

Challenges mix up the normal gameplay with different effects! They last for about 60-80 seconds and appear about every 3-5.3333 minutes (I think), and they come with some new music. Currently, the only effect is Double Lemons. However, ticks popped in challenges do not count towards the next round. Here are some other less interesting changes:

• Ticks won't count towards the next round if they were spawned in previous rounds.
• The Flamethrower doesn't give lemons out anymore
• Changed the music system to fix desyncs and properly switch music at measure switches. 
• Unintentionally made the additional instruments come in exactly when you move to the next round as opposed to on ends of measures.
• Added a ring around the Popper to make it easier to tell when it will pop. This is intended to make the game easier for new players.
• Changed the lemon depletion for the popper from [lemons deplete over time] to [lemons deplete on use]. This also makes the game easier for new players and more directly encourages getting tick combos.