Honor `input_type` Textinput property to choose the type of keyboard

displayed for the TextInput. accompanied with 
https://github.com/kivy/kivy/pull/1543

Fixes https://github.com/kivy/python-for-android/issues/138 by auto setting the type of keyboard to TYPE_CLASS_TEXT|TYPE_TEXT_VARIATION_PASSWORD or 
TYPE_CLASS_NUMBER|TYPE_NUMBER_VARIATION_PASSWORD when password is set to True in a TextInput