Release/1.0-JVM

[Quillraven]

Minor update to the JVM version of Fleks which I will also bring to the KMP branch later on. The changes are:

• Update gradle from 7.3.3 to 7.4.2
• Update Kotlin from 1.6.10 to 1.6.21
• add new getOrNull function to ComponentMapper
• refactor system initialization. onInit is now no longer necessary. The world can be accessed in the normal init constructor block of a system
• update ReadMe to better explain the two different flavors of Fleks and why they are there (KMP and JVM)

With the new getOrNull function it is now possible to write concise code together with Kotlin's let like:

val animations : ComponentMapper<Animation>
// ....
animations.getOrNull(entity)?.let { animation ->
  animation.loop = false
}

I will upgrade Dinoleon to this version and test if everything is still properly working. If yes, then I will prepare a new maven release.