HorizontalCounter Versions Save

I made a post on /r/androiddev about updating this library to Kotlin and @timusus commented that while this was a learning experience, Kotlin would be forced to whoever tried to use the HorizontalCounter, so then I just reverted the changes and updated the "old" .java files to the new feature of custom button icons. So thanks again to him and sorry to you guys.

Now it's possible to add custom drawables for plus and minus buttons!

Changed the main classes to Kotlin! Refactored a few things that should result in better performance

setDisplayingInteger was broken, sorry

This one had a lot of headache involved, but using data binding should be better now

DataBinding is now supported!

Fixed errors with supportsRtl and updated Support Library

Now the values are using Double instead of int as default. You can show integer values by doing this:

app:displayInteger="true"

or this:

horizontalCounter.setDisplayingInteger(true);

Now ready to deploy to JitPack!