Support/Optimize/Fix bugs
- Support: manually change the color of the box [issues35](https://github.com/nachifur/MulimgViewer/issues/35)
- Support: display boxes with different line widths on the zoomed image and the
original image [issues39](https://github.com/nachifur/MulimgViewer/issues/39)
- Support: detects the version and prompts to update the software [issues41](https://github.com/nachifur/MulimgViewer/issues/41)
- Support: hide the top and right toolbars by Ctrl+H [issues42](https://github.com/nachifur/MulimgViewer/issues/42)
- Optimize: the GUI layout
- Fix bug: show RGBA