mime-actions: Group files depending on the opening app

Reinstate the old behaviour which used to look at the files to open, group them by handling application, and pass a single call to each application with all the files it could handle.

For the common case where it's a single application handling all the files, as is usual for handling media files (images, videos, music, etc.), it changes the launching behaviour from: application.bin foo.mp3 application.bin foo2.mp3 application.bin foo3.mp3 to: application.bin foo.mp3 foo2.mp3 foo3.mp3

Revert "mime-actions: launch default uri handlers when activating files"

This reverts commit f5206a6d.

Closes: #117 (closed)