Themes: Use systemui's applied theme for notifications.

Notifications contain RemoteViews which are inflated using the
application's context for which this notification belongs to.  This
can look out of place if SystemUI is using a different theme than the
rest of the system.

This patch will use SystemUIs theme when inflating the RemoteViews,
giving us a more consistent look in the notification drawer.

Credit to @BigBrother1984 for the original cherry pick

Change-Id: I91392c76dca2ef08c82c5ccd68a0f6aca64b647a
Themes: Add icon previews to ThemesContract

Credit to @BigBrother1984 for the original cherry pick

Change-Id: Icbfbee3404702a29881ad4933721d8beb39bef30