recipes-demo: update application's .desktop files for systemd execution

recipes-demo: update application's .desktop files for systemd execution

Initial version of applaunchd with systemd_manager still uses .desktop files
for enumeration purposes and requires DBusActivatable=true to indicate apps
that should be launched as systemd services. This will be addressed in the
new revision of applaunchd and hopefully .desktop files dropped completely.

Bug-AGL: SPEC-4466
Signed-off-by: Denys Dmytriyenko <denys@konsulko.com>
Change-Id: I3bcea79ec653fc834a39be4135ed4c008d5979db