* Replace RIDE_ENTRY_INDEX_NULL with OBJECT_ENTRY_INDEX_NULL
Ride entries are objects like any other, so there is little point having separate constants.
* Use ride_id_t in many more places
* Change RIDE_ID_NULL to 0xFFFF
* Increment network version
* Update replays
Co-authored-by: duncanspumpkin <duncans_pumpkin@hotmail.co.uk>