say "Version Mismatch" when client is ahead server and not compatible.

[rehv]

Issue Description:

I had a problem today on my server, described it on discord and you asked to file a bug report, so...

My server is on pokecube-aio-1.12.2-1.14.6.jar , a few players on my server updated their pokécube version to pokecube-aio-1.12.2-1.15.4.jar on the same profile they use to login to the server, and got a "Fatally Missing Registry Entries" message after trying to connect. It was caused by a "version mismatch", since pokecube-aio-1.12.2-1.15.4.jar adds two sound events for pichu/pikachu.

The "bug" here is not the missing entries, as of course the client shouldn't be allowed to login with missing entities, but rather if it's possible for pokécube to detect and inform the player that something is missing or the server needs updating. Maybe there's a way to automate the build to automatically require/mismatch versions when there are missing registry entries.

I know this is rather minor and will be gone when I update the server jar later this week, so thanks again for your time !

What happens:

-"Fatally Missing Registry Entries" message, leading players to contact support because they don't know better

What you expected to happen:

-Proper version mismatch or some other message.

Steps to reproduce:

1. Install pokecube-aio-1.12.2-1.14.6.jar on a server
2. Install pokecube-aio-1.12.2-1.15.4.jar on the client
3. Try to connect

This is the log generated doing the steps above.

---

Affected Versions (Do not use "latest"): Replace with a list of all mods you have in, if using AIO, list that instead.

• Pokécube AIO: pokecube-aio-1.12.2-1.14.6.jar server, pokecube-aio-1.12.2-1.15.4.jar client.
• Minecraft: 1.12.2
• Forge: 2838