Reduce code repetition

[qixils]

A lot of effects have a lot of needless repetition that could be solved with some abstraction, such as the health commands and especially the enable/disable keep inventory commands. Some more API classes should be created similar to the entity mapper which reduce the repetition of code. If some functionality is too niche to add to the general wrapper API, it could still be abstracted out with, well, an abstract command class. This will likely make a Sponge 9 implementation (if necessary) a lot cleaner and generally make it easier to fix bugs