JSON Support for ISM

[daheise]

I have been working on an update to the mod.json to enable support for ISM, since the ISM file on Nexus seems to have gotten out of sync. I'm not confident enough in my work, or where/if it belongs in your repo to issue a PR. You can view it here.

Here are issues I am not sure how to clean up/validate.

1. How do I know a faction is safe to leave out of the "FactionTags", e.g. can I leave out HostileMercenaries?
2. Do need to add a tag for each faction to FactionShopItems and FactionShops like for FactionTags? Will it cause issues if they're in any of these places but those faction shops aren't implemented?
3. Is FactionStrings dead code? I don't have it in this json but it's easy to add back.