sdk: notification: allow forcing notification color for preview

Parts uses notifications to preview custom notification lights.
Since Android O we got NotificationChannels and the internal API uses
the color values of the channel instead of the color set at the notification.

To prevent unexpected breakage in future, introduce a flag to be used for
providing preview colors in a bundle to force said color.

Also introduce flags to control the ON and OFF duration.

Change-Id: Ifbb7995a19d95b6ddb2627c1b14dd201f9dc5430
Signed-off-by: Alexander Martinz <amartinz@shiftphones.com>