Ensure updated file integrity

[slotthhy]

When creating a Penumbra mod, there should be some sort of checksum or hash of the modded file contents in order to determine if a file has been changed by an update. For example if we get into more complex mods, such as EXD, we will want to disable those if the game changes them, or retail will crash or exhibit unexpected behavior.

On the Penumbra end, this would simply be ensuring the checksum for the mod matches the contents of the game's file. The mod creation software (Umbra?) will be responsible for creating the checksum.