Inefficient deletion in the folders dialog

[ghost]

from email:

FOLDER SELECTION WINDOW:

When DG comes up and the folder selection window opens you cannot select-all and slap the delete-key or otherwise clear-all.
You cannot delete items using the keyboard but are forced to use the dialog buttons.
You cannot delete more than one item at a time.

[ghost]

(from [dab922d2d523]) [#179] Pushed the delete-or-exclude folder down from GUI layers to the core.
https://bitbucket.org/hsoft/dupeguru/changeset/dab922d2d523/

[ghost]

(from [7ed7279e96b4]) [#179] Refactored folder deletion so that it uses selection in the core's directory_tree instead of using the one from the GUI layer.
https://bitbucket.org/hsoft/dupeguru/changeset/7ed7279e96b4/

[ghost]

(from [38c760ec050a]) [#179 state:fixed] Added multiple-selection to the folder selection dialog and thus added the ability to remove multiple folders at once.
https://bitbucket.org/hsoft/dupeguru/changeset/38c760ec050a/

[ghost]

(from [35642ef7ce3f]) [#179] Fixed a crash under Cocoa when deleting many folders at once.
https://bitbucket.org/hsoft/dupeguru/changeset/35642ef7ce3f/