appimaged: Handle opening AppImages when Firejail is installed

[probonopd]

When downloading files using the browser, then opening the downloaded AppImage through the browser does not work (because when firejail is available, then appimaged does not set the executable bit).

This could be changed by registering the AppImage type-1 and type-2 MIME types with a helper script that would run the AppImage file using firejail.

Potentially the functionality could even be added to appimaged which already has most of the logic for determining how to run an AppImage with firejail in place - pull requests welcome!

[TheAssassin]

AppImageLauncher could perfectly implement this, as it does already intercept any launch of AppImages. appimaged can never implement such a feature due to how it works. I would close this issue here, and rather move on to AppImageLauncher for this feature.

[probonopd]

Please feel free to mirror this issue to AppImageLauncher, but please don't close it here just yet.

[TheAssassin]

All I'm saying is that appimaged can't do it, technically.

[probonopd]

Unless we make it to do it, perhaps by merging all of those 3 launcher thingies into one. :-)

[TheAssassin]

@probonopd that's the master plan isn't it?

I could also argue that appimaged has its own issue tracker now...