Prevent accidentally deleting files

Right now it is really easy to accidentally delete files:
-Deletion can not be undone
It is not immediately clear that right Click>remove on a selected file will remove all selected files.
-The “are you sure?” dialog does not specify the number of items to be deleted.
-It is very easy to have some file selected and forget about it.

(from redmine: issue id 2325, created on 2016-04-21 by root, closed on 2016-05-04)

• Changesets:
  • Revision 2829 by Fabian Heidemann on 2016-05-04T16:14:02Z:

[file] add number of files to remove dialog, fix #2325

• Revision 2829 by Fabian Heidemann on 2016-05-04T16:14:02Z:

[file] add number of files to remove dialog, fix #2325

• Revision 2838 by Fabian Heidemann on 2016-05-04T16:14:02Z:

[file] add number of files to remove dialog, fix #2325

• Revision 2838 by Fabian Heidemann on 2016-05-04T16:14:02Z:

[file] add number of files to remove dialog, fix #2325