New Upgrade & UI changes

New Features

• A new upgrade! Spawn rats of a higher tier!
• Shop buttons now change colour based on if you are able to buy them.

Bugfixes & Changes

• Buying rats will no longer let you go over number of maximum rats.
• Upgrades now have a limit as well. No longer infinite upgrading.
• UI panels now use a script instead of setActive to toggle visibility.
• Fixed Android not saving progression.