Include Bash completion script in AppImage, upload to bintray

[schuhschuh]

The Bash completion script for mirtk would be handy to have when using the AppImage from bintray...

[schuhschuh]

The Bash completion script for docker-mirtk is available in the AppImage. To access it, one has to extract the image content with mirtk --appimage-extract.

To-Do: Upload this file to bintray for direct download.