Introduces a group of Things as a construct for bundling Things that should constitute a single unit for whatever reason. One reason could be to make an _item set_ an atomic reward, e.g. a set of diamond tools for beating the `workshop` arena. Instead of having to spread the rewards out into multiple waves or use a different plugin to create item groups, this component allows MobArena to support that kind of intent natively. Note that nothing is wired up in this commit, so really this commit is just introducing unused code.
MobArena 
MobArena is an arena-style minigame for Spigot-based Minecraft servers
Getting Started
If you don't want to compile the plugin yourself, grab a release artifact from one of these two sites:
The wiki here on Github should have all the information you need to get started using the plugin.
Getting Help
If you run into problems or need help with something, feel free to hop on the MobArena Discord server to have a chat: Instant Invite
Remember, though, that this communication channel is idle chat, which means you likely won't get a response immediately. It could take anything from a couple of seconds to a day, but your message will be seen.
Contributing
Found a bug, got a suggestion, or want to dig into the code base? There are many ways to contribute to the project!
Get started here: Contributing