General improvements to GT Module Code

[TechLord22]

What

Makes some general improvements to the GT Module code.

1. Adds annotations to method signatures and some fields to improve nullity clarity
2. Uses clazz.getConstructor().newInstance() instead of clazz.newInstance(), since it's deprecated in Java 9, and can throw hidden checked exceptions previously not accounted for.
3. Fixes a bug where the last active module container is treated as active between initialization events, and indefinitely after the last event.
4. Improves some error messages for improper module API usage.
5. Makes some other general code improvements, such as using FastUtil collections.

Outcome

Improves GT Module related code.