Gallery2: Split DDM loading into two parts to hide latency

Split DDM loading into two parts: parsing and loading.
Filter categories will be available once parsing is done.
Ladoing of DDM will continue to happen in the background after
parsing is complete.
When the user selects the dual camera filter category, we will
show a loading dialog if DDM loading is not yet complete.

Conflicts:
	src/com/android/gallery3d/filtershow/category/MainPanel.java

Change-Id: I5c7b454f0dcf00989d4bb0bbe95735b67785284d