Fix crash when receiving SMS before finishing registration.

If someone has set Signal as the default SMS but has cleared data or
otherwise reset the app's storage state, it can get into a weird
situation. Notably, it'll crash because SmsReceiveJob.onRun() expects
Recipient.self() to be available.

However, it also makes it impossible to get the registration SMS,
because the app won't post a notification for the code.

This change will post notifications and SmsRetriever broadcasts for
relevant SMS messages.

app/src/main/java/org/thoughtcrime/securesms/notifications/NotificationIds.java

@@ -7,6 +7,7 @@ public final class NotificationIds {
   public static final int MESSAGE_SUMMARY       = 1338;
   public static final int APPLICATION_MIGRATION = 4242;
   public static final int SMS_IMPORT_COMPLETE   = 31337;
+  public static final int PRE_REGISTRATION_SMS  = 5050;
   public static final int THREAD                = 50000;
 
   private NotificationIds() { }