82 - Finish mod system

[yogwoggf]

Ticket

Resolves #82

Changes

• Rewrites the mod manager
• Adds a mod repository, which is a wrapper over a new SQL table which attaches metadata to a mod ID, allowing custom properties invariant of the actual mod (like enabled state, possibly mod configs later on?)
• Updates the mod schema.
  • ID - a string specifying the mod's internal identifier. Ideally this is in kebab case (like-this).
  • Weapons - an array (lua table) of weapons that are directly associated/registered by the mod independently of Gelly. That is, if you're making a goo blaster, you would add the goo blaster's class name to this list.
  • Entities - an array (lua table) of entities that are directly associated/registered by the mod independently of Gelly. Similarly to weapons, if you were making, say, a faucet, you'd add that faucet's class name to this list.
• Restricts disabled mods from appearing in the spawn menu
• Adds a command line interface for interacting with the mod manager
  • This is currently the primary entrypoint for selecting mods. I'll raise a ticket for a mod menu, but as you might tell, it could end up being another major ticket since I don't expect that UI to be simple.
• Adds the functional-arrays utility library, a wrapper over lua arrays to enable concise functional programming.
• Fixes the .luarc.json to make it resolve our modules correctly.
• Fixes the particle radius not working correctly in the Gelly Preset Creator.
• Updates changelog and version to 1.9.0
• Added clientside entity deletion function

Other

There are about three out-of-scope fixes (last 3 in the Changes section). I think they are excusable since they all are very small changes (1-2 line changes).

[yogwoggf]

Will do a self-review, maybe even a real code review given the magnitude of this PR.