support output 4K video file for the slideshow

Support the latest macOS Catalina
Support the dark mode of macOS
Fixed some bugs

1. Add video clips to slideshow
2. Adjust volume of background and video clips
3. Improve stability and performance
4. Remove features of uploading Youtube and Facebook

1. Retina display supported
2. Some bugs fixed

1. Add mp4 video output format.

Add synchronization feature of music and slideshow

Improve encoding video quality.