Adding a couple memory optimizations to Launcher

-> Always dispose of widget page views when leaving the activity.
   These pages hold onto many bitmaps.
-> Clear database cache when leaving the activity.

Bug: 17967108
Change-Id: I10ebaaed14e7cd86f09a9afcabd73043705f21b8
diff --git a/src/com/android/launcher3/PagedViewWithDraggableItems.java b/src/com/android/launcher3/PagedViewWithDraggableItems.java
index 2a29c33..7f4a3a0 100644
--- a/src/com/android/launcher3/PagedViewWithDraggableItems.java
+++ b/src/com/android/launcher3/PagedViewWithDraggableItems.java
@@ -91,6 +91,10 @@
         return super.onTouchEvent(ev);
     }
 
+    public void reset() {
+        mLastTouchedItem = null;
+    }
+
     @Override
     public boolean onTouch(View v, MotionEvent event) {
         mLastTouchedItem = v;