On-The-Spot: Add information on how to reset preferences

Info is added to the main On-The-Spot preference dialog.
(As suggested by +Carlo Savignano)

PS 2:
* delete unneeded code

PS 3:
(https://dl.dropboxusercontent.com/u/90317107/on_the_spot_pref_helper.png)
* Unclutter OTS Dialog

Change-Id: Iaf4f67e4b03babd1d6a604c2524781a748dd8025
Signed-off-by: kajuten <julian.kaltenhofer@gmail.com>