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

Info is added to the main On-The-Spot preference dialog.
https://dl.dropboxusercontent.com/u/90317107/on_the_spot_pref_helper.png
(As suggested by +Carlo Savignano)

I have one improvement in mind.
It would be nice to make the reset hint title ("To reset preferences:")
clickable to toggle the more informative reset message.
(Similar to the permission overview in the Play Store)
But I'll need some time to read more on how to do that.

PS 2:
* delete unneeded code

Change-Id: Iaf4f67e4b03babd1d6a604c2524781a748dd8025
Signed-off-by: kajuten <julian.kaltenhofer@gmail.com>
Conflicts:
	core/res/res/values/pa_strings.xml
	core/res/res/values/pa_symbols.xml