FrozenLib

- Updated `InterpolatedGravityFunction` to now properly supply a bottom and top gravity value.
- Multiple `GravityBelt`s can now apply at the same position.
- Reworked a few aspects of the File Transferring system!
  - File transfers can now have a much larger size, thanks to `FileTransferPacket` now being able to split into multiple packets.
  - The `FileTransferFilter` class has been added, filtering out file transfers/requests that are not whitelisted.
    - Only `.png` and `.json` files can be accepted by file transfers/requests. This is hardcoded.
    - By default, no destination paths are whitelisted.
      - Destination paths can be whitelisted separately on the server and client.
      - A destination path can be whitelisted using the `whitelistDestinationPath` method.
      - Players sending a file with a file extension or destination path that isn't whitelisted will instantly be kicked from the server.
    - By default, no request paths are whitelisted.
      - Request paths can be whitelisted separately on the server and client.
      - A destination path can be whitelisted using the `whitelistRequestPath` method.
      - Players requesting a file with a file extension or request path that isn't whitelisted will instantly be kicked from the server.
- Added `RelativeMovingSoundInstance`, a type of `SoundInstance` that will move alongside the player with an offset.
- Fixed a crash upon booting servers.