Adjust wallpaper during B&R to center align

This CL implements the alogirithm to correctly restore the wallpaper's center point from devices with different aspect ratios (during B&R).
 The algorithm involves first computing the original crop of the user (without parallax).
 Then manually adjusting the user's original crop to respect the current device's aspect ratio (thereby preserving the center point).
 Then finally, adding any leftover image real-estate (i.e. space left over on the horizontal axis) to add parallax effect.

Flag: NONE
Bug: 328234087
Test: http://ab/I00700010262844212
Change-Id: I706f955ae54b570af04235d2e0548d1570e5ac6b