uix:TextInput fix changing selection using selection_handles. closes #2006
uix:TextInput make selection handles display only when selection is
done.
uix:TextInput only fade in handles if they aren't already visible
uix:TextInput make selection handles follow widget position.
uix:TextInput account for widget pos for selection handles
Update textinput.py
uix:TextInput update selection handles on window move and account for
widget position. Closes #2012 and #2013
uix:textInput selection_handles account for size changes
uix:TextInput update handles on selection change
uix:TextInput revert selection_handle images to their previous state
Merge pull request #2008 from kivy/selection_handles

Selection handles