[496582] Consider preferences scope hierarchy

Make sure we use either the platform's IPreferencesService or the
relevant IPreferenceStore when reading and writing preferences
everywhere in EMFCompare.

Bug: 496582
Change-Id: I2cbdf6f9356eafba867f0473f680429d0ae6cd35
Also-by: Mathias Schaefer <mschaefer@eclipsesource.com>
Also-by: Philip Langer <planger@eclipsesource.com>
Signed-off-by: Laurent Delaigue <laurent.delaigue@obeo.fr>
34 files changed