Major Loader Rework

[TheCodedOne]

Note: This PR is still WIP, bear in mind when reviewing that some aspects have only partly been converted to the reworked system.

This rewrites a large portion of the Loader, enabled by the API rework in SandboxPowered/SandboxAPI#40 API changes are described there.

Goals and complete aspects of this PR

• [x] Move minimum required Java version to 11
• [x] Move to a modular design for implementations to use.
• [ ] Implement full Forge support
• [ ] Move implementation communication to dependency injection

Closes #20