Send to trash: add an option to delete all files

[bennygui]

For this bug: http://thread.gmane.org/gmane.comp.graphics.darktable.devel/6889

[LebedevRI]

Adds new string, probably a feature(?) => will have to wait until after 2.0

[bennygui]

@LebedevRI I'm letting you decide what is best... but from the thread, the person who reported this said: "As a person, who had to click the button 50+ times I would prefer having
an untranslated string :)"

Anyway... It will probably not affect many users.

[houz]

What about a checkbox "remember the choice" or "don't ask again" (or something like that) which just remembers whatever you click for that job. It would allow deleting them all, but also to just remove all of them from the collection. Or whatever someone wants.

[bennygui]

I'm not sure it's worth putting a lot of effort into: this dialog will almost never pop except if you have weird file permissions or if trashing is disabled on the system or the filesystem.

[TurboGit]

Is that still needed? If so, can this be rebased and retested on current master? Thanks.

Otherwise let me know and I'll close this PR. Thanks.

[rahbek1]

I would like this improvement.
All my images are located on a NFS mount. Whenever I try to delete an image I get this message: "Trashing on system internal mounts is not supported."

I guess that more people will run into this issue since NFS and CIFS was added to the list of system internal filesystems
https://gitlab.gnome.org/dsd/glib/commit/d1eaf72c001279aa15a2135a0749ef864c8edb42
https://gitlab.gnome.org/dsd/glib/commit/0d69462f146071ee4ad1407f9d9ac56f65c9d485

[TurboGit]

Merged manually fixing the conflicts. Tested and working as expected. Thanks.