Separating methods for updating the model to a sepatate class.

Removing static access to model update methods, to allow for better
access control and testing

Change-Id: I9afe004dbf1b2fe50df422fd28bceea9230a4704

src/com/android/launcher3/folder/FolderPagedView.java

@@ -336,7 +336,7 @@ public class FolderPagedView extends PagedView {
                     info.cellY = newY;
                     info.rank = rank;
                     if (saveChanges) {
-                        LauncherModel.addOrMoveItemInDatabase(getContext(), info,
+                        mFolder.mLauncher.getModelWriter().addOrMoveItemInDatabase(info,
                                 mFolder.mInfo.id, 0, info.cellX, info.cellY);
                     }
                 }