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

proguard.flags

@@ -97,30 +97,19 @@
 # support jar.
 -keep class android.support.v7.widget.RecyclerView { *; }
 
-# LauncherAppTransitionManager
--keep class com.android.launcher3.LauncherAppTransitionManagerImpl {
+# Preference fragments
+-keep class ** extends android.preference.PreferenceFragment {
     public <init>(...);
 }
 
-# InstantAppResolver
--keep class com.android.quickstep.InstantAppResolverImpl {
-    public <init>(...);
-}
-
-# MainProcessInitializer
--keep class com.android.quickstep.QuickstepProcessInitializer {
-    public <init>(...);
-}
-
-# UserEventDispatcherExtension
--keep class com.android.quickstep.logging.UserEventDispatcherExtension {
+## Prevent obfuscating various overridable objects
+-keep class ** implements com.android.launcher3.util.ResourceBasedOverride {
     public <init>(...);
 }
 
 -keep interface com.android.launcher3.userevent.nano.LauncherLogProto.** {
   *;
 }
-
 -keep interface com.android.launcher3.model.nano.LauncherDumpProto.** {
   *;
 }