CM11 Themes: load wp from apk if uri is null

When setting a default theme on first start, the provider may
not have processed the theme and the uri for the wp will be null.
If this happens try to load the wallpaper from the themes assets.

Change-Id: I883b9dd796920e66e4729e78d41cd8899916fa42
Themes: Map themed icon to app after upgrade

Before this patch, applying an icon theme and then upgrading an app would
cause the app to lose its themed icon.

Change-Id: Ia76a33d0fb731720aa735e9dd9596bc5d2e75d9f
add a getter for the x and y offsets of the wallpaper window

Change-Id: I35294bcac664e85cc5d344b50b5c4335a60d3f37