Use a dialog for the welcome page. Thus the startup sequence

consists of three dialogs.
Rename to HelpActivity.
Fix activity button styles.
Reuse EulaDialogFragment when invoked from the AboutDialogFragment.
Only hide the title bar on the TrackDetailPage.

MyTracks/src/com/google/android/apps/mytracks/fragments/DeleteAllDialogFragment.java

@@ -26,10 +26,14 @@ import android.os.Bundle;
 import android.support.v4.app.DialogFragment;
 
 /**
- * Delete All DialogFragment.
+ * A DialogFragment to delete all tracks.
+ * 
+ * @author Jimmy Shih
  */
 public class DeleteAllDialogFragment extends DialogFragment {
 
+  public static final String DELETE_ALL_DIALOG_TAG = "deleteAllDialog";
+  
   @Override
   public Dialog onCreateDialog(Bundle savedInstanceState) {
     return DialogUtils.createConfirmationDialog(getActivity(),