Add a setter/getter for Launcher.mAllAppsButton.

Also, handle clicks on the all apps button by using onClick() method in
Launcher instead of directly calling onClickAllAppsButton in Hotseat.java

Bug 12553852
Change-Id: I261c27d3e964bbb1f52c2ab610997defd99a59bd
diff --git a/src/com/android/launcher3/Launcher.java b/src/com/android/launcher3/Launcher.java
index bd1ef32..f1ce235 100644
--- a/src/com/android/launcher3/Launcher.java
+++ b/src/com/android/launcher3/Launcher.java
@@ -1334,6 +1334,17 @@
     }
 
     /**
+     * Sets the all apps button. This method is called from {@link Hotseat}.
+     */
+    public void setAllAppsButton(View allAppsButton) {
+        mAllAppsButton = allAppsButton;
+    }
+
+    public View getAllAppsButton() {
+        return mAllAppsButton;
+    }
+
+    /**
      * Creates a view representing a shortcut.
      *
      * @param info The data structure describing the shortcut.