Better depth map versioning

[laplamgor]

Use hash (e.g. MD5) instead of version number for depth map download URL

Currently, the custom depth maps in this repo were versioned using in-game version numbers.
It requires a manual commit to update the version number when there are any Seasonal CG changes.
The version number does not match even if the same depth map existed in the server / repo.

Using hash also help deduplicate depth maps of ship IDs with same CG (some ships no-kai vs kai)