updated to rc 16 and added annotations

[J3fftw1]

Short Description

Updated to rc 16 and added annotations

Additions/Changes/Removals

Updated to rc 16 and added annotations

Related Issues

N/A

Checklist

• [x] I have fully tested the proposed changes and promise that they will not break everything into chaos.
• [x] I have also tested the proposed changes in combination with base Slimefun and made sure nothing breaks/unexpected happens.
• [x] I followed the existing code standards and didn't mess up the formatting.
• [ ] I did my best to add documentation to any public classes or methods I added which may not be obvious to maintainers.
• [x] I have added Nonnull and Nullable annotations to my methods to indicate their behaviour for null values