Fix PPI default value

• Fixed bug where PPI would save the encode threads value instead of the entered PPI value

PPI and Alpha Channel Support

• Added option to specify output files PPI
• Added option to strip alpha channel from files
• Added support to open .jpeg files

Unix path bugfix

• Fix path issue on non-windows platforms

Avalonia Port

• Rewrote GUI in Avalonia for cross-platform
• Added builds for Linux and OSX
• Small fixes to grayscale file conversion

Minor changes

• Added icon
• Added toggle for TTA mode
• Added selectors for GPU thread counts
• Added tooltip

Use ImageMagick for grayscale

• Switch grayscale feature to use ImageMagick
• Added in-GUI log display