Convert to gradle

[S-Numan]

This was a bit fiddly to setup.
I removed a bunch of things which I was unaware of their purpose, will want to confirm that nothing important was removed.

This allows MagicLib to be opened by anyone by simply opening it in Intellij IDEA, no setup needed aside from the mod dependencies. Theoretically.

Use the gradle package_mod to make a release to give to others.

This also removes the github actions. I like them, but I see several issues.

1. I would like to avoid storing the /jars on the github outside of the releases. They cause larger files sizes for every time they're committed and show up as a stage-able file which can be troublesome especially when switching branches. The only time they're actually needed is when I'm making a release.
2. package_mod exists to package the mod already. With github actions it was inconvenient as every time I wanted to share a dev/test release I had to manually remove files. I suppose I could've not, but sending unneeded files bothers me.
3. I have to edit the description of the release made anyway to add the change-log no?