Dependencies and cleanup

[TacoTheDank]

Oh boy it's that time again.

1st commit

• Your friendly neighborhood Gradle wrapper update (5.6.1 -> 6.2 changelog)

2nd commit (Look over the changelogs to see if there's any new features you might want to use)

• Buildtools 29.0.2 -> 29.0.3 changelog
• ExoPlayer 2.11.1 -> 2.11.3 changelog
• OkHttp 4.3.1 -> 4.4.0 changelog
• Jsoup 1.12.1 -> 1.12.2 changelog
• Android-Gif-Drawable 1.2.17 -> 1.2.19 changelog
• EventBus 3.1.1 -> 3.2.0 changelog
• Flexmark 0.50.50 -> 0.60.2 changelog
• RxJava 2.2.12 -> 2.2.17 changelog (There's also the option to migrate RxJava 2.x to 3.x if you want to think about taking that on, otherwise we can just stick with 2.x)
• We don't need transitive dependencies, in retrospect I don't know why I added those

3rd commit

• Cleaned up a bit of Kotlin

[Adamantcheese]

Actually migrating to RxJava 3 would go completely smoothly as we don't do anything particularly complicated. @K1rakishou your tests would need to be updated to account for this information (notably getEvents was removed), as you use it in almost every test: https://github.com/ReactiveX/RxJava/wiki/What%27s-different-in-3.0#test-support-methods

[K1rakishou]

notably getEvents was removed

Noooo.

But I guess we can try switching to 3.0. There were some API changes so a little bit of refactoring is expected.

I guess we could extract it into a separate task.

[K1rakishou]

Oh by the way

OkHttp 4.3.1 -> 4.4.0 changelog

This may actually help with problems some people are experiencing with images refusing to start getting downloaded.