tmf: Fix copy trace handler enabled in unrelated dialogs

tmf: Fix copy trace handler enabled in unrelated dialogs

Ctrl-C no longer opens the Copy Trace dialog from another dialog when
the current selection in the Project Explorer is a trace element.

The same fix is applied to the copy experiment handler.

Change-Id: I4eb9df578d2227b74312d7fe660b2a3caf2b2627
Signed-off-by: Patrick Tasse <patrick.tasse@gmail.com>
Reviewed-on: https://git.eclipse.org/r/34415
Tested-by: Hudson CI
Reviewed-by: Bernd Hufmann <bernd.hufmann@ericsson.com>
Tested-by: Bernd Hufmann <bernd.hufmann@ericsson.com>