Added Search For Countries

[FazalHussain]

Added Search For Countries

Usage

private fun showCountryDialog() {
    val countryPicker =
            CountryPickerDialog(this,
                    CountryPickerCallbacks { country, flagResId ->
                        countryPickerTv.text = country?.dialingCode.toString()
                    })
    countryPicker.show()
    val window: Window? = countryPicker.window
    window?.setLayout(MATCH_PARENT, MATCH_PARENT)
}