- fix issue 11.
- improve cursor draw speed by using restore_region method.
- fix some visual aspect with zoom box action (image border + small rectangle position).
- When pan/zoom, left axis width doesn't change in fast draw.
- In main.py, don't used 'disable_on_activity' when platform is android (avoid wrong touch behavior).
- Rename some graph_widget name to make it worked with pip install.