Improve code coverage

[utybo]

Thankfully, because Shedinja's internals are "open" by design and easy to mess around with, testing them is also pretty simple. It just needs to be done.

• Add JaCoCo (note that Kotlin inline functions are not marked as covered jacoco/jacoco#654 gets in the way)
• Add tests where relevant.

Module	Priority	Why ?
shedinja	High	Core classes need to be tested to ensure that their behavior does not shift too much in the future.
shedinja-test	High	shedinja-test is a very important brick of any Shedinja application and should be tested as such.
shedinja-services	Medium	Although important, services are usually pretty easy to debug and straightforward. Testing is important but not as much as others.
shedinja-koin-*	Low	Koin support is a hack upon a hack. It is quintessentially unreliable and hacky, and cannot be reliably tested.

[utybo]

Fixed by #22