Validation needed on data files

[verhoevenv]

Data files might be internally inconsistent. We should be able to easily validate if a mod is consistent.

I see two ways:

• Create a different tool for this, maybe in a scripting language
• Do the validation inside of Notrium, and report any errors after loading a mod. This might even crash Notrium, as a player (non-modder) should not see such messages

[Enet4]

I would go for the second way, but I don't agree with crashing here, as the player could still be a non-modder if by any chance the mod was corrupted by mistake of the modder, or if the player installed it incorrectly. We should instead let the program show something like "Failed to load mod «mod_name». See log file for details"