add a helper extension for listening to viewpager page changes

        propMinSdkVersion = 16

        propTargetSdkVersion = propCompileSdkVersion

        propVersionCode = 1

        propVersionName = '3.13.19'

        propVersionName = '3.13.20'

        kotlin_version = '1.2.21'

        support_libs = '27.0.2'

    }

package com.simplemobiletools.commons.extensions

import android.support.v4.view.ViewPager

fun ViewPager.onPageChangeListener(pageChangedAction: (newPosition: Int) -> Unit) =

        addOnPageChangeListener(object : ViewPager.OnPageChangeListener {

            override fun onPageScrollStateChanged(state: Int) {

            }

            override fun onPageScrolled(position: Int, positionOffset: Float, positionOffsetPixels: Int) {

            }

            override fun onPageSelected(position: Int) {

                pageChangedAction(position)

            }

        })