uix: TextInput improve visual polish and mninor performance improvements
- Use `sp` conversion to set size for bubble closes #1065
- Add animation to sut copy paste dialogue
- position `cut copy paste`bubble so that it appears above/below the
  finger not obscured by it.
- add `selectall` option to paste bubble.
- minor speed improvements for cursor movements.
- use unique cid for text_width(no body noticed a issue with this?)
Merge pull request #1069 from kivy/textinput_improvements

uix: TextInput improve visual polish and mninor performance improvements