Improve QR code workflow slightly

* Improve wording so contacts know they need meet up to scan
  and scan each other's codes
* Use consistent progress bar styles

briar-android/src/org/briarproject/android/keyagreement/ShowQrCodeFragment.java

@@ -337,7 +337,7 @@ public class ShowQrCodeFragment extends BaseEventFragment
 		listener.runOnUiThreadUnlessDestroyed(new Runnable() {
 			@Override
 			public void run() {
-				status.setText(R.string.waiting_for_contact);
+				status.setText(R.string.waiting_for_contact_to_scan);
 			}
 		});
 	}