Cleaning up build rules to simplify customizing derivative projects

> Using {packageName} instead of hardcoding com.android.launcher3 in AndroidManifest.xml
  for strings which are dependent on packageName
> Adding proguard rule to prevent obfuscating any overridable class
> Making it easier to extend SettingsActivity by overriding the fragment class

Change-Id: I5668c3f33b4cf20ad01d7f54b3d79cc0d268d391
diff --git a/src/com/android/launcher3/LauncherAppTransitionManager.java b/src/com/android/launcher3/LauncherAppTransitionManager.java
index 4037a23..970e558 100644
--- a/src/com/android/launcher3/LauncherAppTransitionManager.java
+++ b/src/com/android/launcher3/LauncherAppTransitionManager.java
@@ -23,13 +23,15 @@
 import android.graphics.drawable.Drawable;
 import android.view.View;
 
+import com.android.launcher3.util.ResourceBasedOverride;
+
 /**
  * Manages the opening and closing app transitions from Launcher.
  */
-public class LauncherAppTransitionManager {
+public class LauncherAppTransitionManager implements ResourceBasedOverride {
 
     public static LauncherAppTransitionManager newInstance(Context context) {
-        return Utilities.getOverrideObject(LauncherAppTransitionManager.class,
+        return Overrides.getObject(LauncherAppTransitionManager.class,
                 context, R.string.app_transition_manager_class);
     }