tmf: Improve Delete Supplementary Files command

tmf: Improve Delete Supplementary Files command

- Make all checkbox elements checked by default in the dialog

- Allow multiple selection as long as at least one of the selected
elements has supplementary files

- Update trace handler to support both traces and experiments, and
delete the experiment handler

- Ensure supplementary files for a particular trace are only shown once
in the list (e.g. same trace selected both under Traces folder and under
experiment, or two experiments selected that contain the same trace)

- Ensure only traces and experiments that have supplementary resources
to delete have their editors closed, and that their project is refreshed
only once.

Change-Id: I91f823c67c15da699c815fdf9daf9cfec5082ec9
Signed-off-by: Patrick Tasse <patrick.tasse@gmail.com>
Signed-off-by: Alexandre Montplaisir <alexmonthy@voxpopuli.im>
Reviewed-on: https://git.eclipse.org/r/25858
Tested-by: Hudson CI