[Phone] Don't use custom shared preferences

Just use the app-wide default shared preferences, so that it'll read from the
cache rather than the filesystem.
The default shared preferences should be preloaded by
ContactsApplication.onCreate using a worker thread when Dialtacts needs it.

It was actually a strict mode violation causing something like > 100ms penalty,
but I assumed it was beacuse it was the first read and unavoidable.
I hadn't realized dialtacts had its own preferences.

I also fixed the social widget settings.  Existing settings will all be
migrated.

Also fixed the log spew from SocialWidgetSettings.

Bug 5296990

Change-Id: Idb8e393ebfd6c77b14906ea4ee26dfd032da2770