Conveyor Belts (Fabric)

- Replaced models for up and down slopes from blocky to smooth. Block versions will be available through a resource pack.

- Fixed bug where top half of sloped belt would move player when bottom half not enabled.

- Fixed a visual bug where fully saturated downward sloping belts would not display the item's movement progress correctly as would sometimes use the fully completed progress of the item before.

- Removed unused mixin reference from fabric.mod.json

- Items displayed on sloped belts match gradient
- When placing downward sloping belts towards self, they will be placed from the top half
- Fixed bug where placing sloped belts could remove blocks above them

- BlockItem into own class for future changes (rendering direction belt will be placed while holding)