Move e2e tests into Slimefun

[WalshyDev]

For the MVP, we created the tests within this project. These need to live within Slimefun.

Things to solve:

• How do we tell this plugin to run the tests (and which package they live in)?
• How do we ensure/force the plugin class loader to have the e2e tests
  • Currently we have a hack to do this:

  • e2e-tester/src/main/java/io/github/slimefun/e2etester/framework/TestFramework.java

    Line 42 in cf66d8c

    new Startup();

  • However, we'll need to get rid of this

The main goals of this are to allow this tool to be re-used by other plugins and make sure our tests stay together (within SF repo).