Kotlinize fragments

[cortinico]

Please note that this PR contains breaking changes.
I've kotlinized all the Fragments in the library.

Moreover, I cleaned up the exposed Api for AppIntroFragment and AppIntro2Fragment. Now they expose only two methods:

• newInstance(SliderPage) as before
• A @JvmOverload-ed method like this

newInstance(
                title: CharSequence? = null,
                description: CharSequence? = null,
                @FontRes titleTypefaceFontRes: Int = 0,
                @FontRes descTypefaceFontRes: Int = 0,
                @DrawableRes imageDrawable: Int = 0,
                @ColorInt bgColor: Int = 0,
                @ColorInt titleColor: Int = 0,
                @ColorInt descColor: Int = 0
        )

This will cover the majority of the use cases. I saw that we had several @deprecated methods, plus other non deprecated newInstance methods with a permutation of those parameters.

I generally like the two classes now as they're smaller and cleaner. But I'd love to discuss how much aggressive we want to be with removal of old APIs

[cortinico]

ping @paolorotolo 👋

[paolorotolo]

Hey @cortinico sorry for the delay! I'm ok being aggressive on old APIs and have classes cleaner thanks to Kotlin features.
We just have to make sure to update all the needed docs before next release.