Adjusted background task TimeTrigger from 15 to 10 minutes

Changed timer from 15 to 10 minutes to better coincide mathematically
with common intervals that people will probably pick.
Refactored settings

Refactored settings to put common logic in two helper functions. This
simplifies set up time of any new settings that need to be added.
Added Settings page, wired it up

Wired to new setting in the framework. Added reference to
WinRTXamlToolkit to get a number picker, it sucks, but works for now.
Addition of settings page brought in some helper classes.
Removed hard-coded timeout values

Removed hard-coded values and replaced them with look-up to setting
value.