v1.2.0

New features/fixes:

• Bundle ffmpeg
• Implement partial speed control - J, K, L, however backward playing is not supported by chromium.
• Add support for more formats by detecting format and using same form as for input file (don't always use mp4). for instace WEBM now works.
• Improve ffmpeg error handling
• Improve react rendering a bit
• Icon
• Fix menus on windows