update v39.3

The gym is the last one to get a revamp, after that I'll add some new stuff until we hit the 400th!
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- Revamped the gym Ball (4 colors)
- Revamped the gym mirror (2 sizes) and added a modular version
- Revamped the dumbbels and added 3 new sizes and 1 recolor for each (8 types total)
- Added a gym disc and a stacked version of it

*Everyone who already bought the asset can get the new stuff for free

See you and happy game-making! :)