Make system database import notification translatable

Also replace "TextSecure" with "Signal" in the notification text.

Closes #5256
// FREEBIE

res/values/strings.xml

@@ -594,6 +594,8 @@
     <!-- ApplicationMigrationService -->
     <string name="ApplicationMigrationService_import_in_progress">Import in progress</string>
     <string name="ApplicationMigrationService_importing_text_messages">Importing text messages</string>
+    <string name="ApplicationMigrationService_import_complete">Import complete</string>
+    <string name="ApplicationMigrationService_Signal_system_database_import_is_complete">Signal system database import is complete.</string>
 
     <!-- KeyCachingService -->
     <string name="KeyCachingService_signal_passphrase_cached">Touch to open.</string>

src/org/thoughtcrime/securesms/service/ApplicationMigrationService.java

@@ -188,8 +188,8 @@ public class ApplicationMigrationService extends Service
     public void onReceive(Context context, Intent intent) {
       NotificationCompat.Builder builder = new NotificationCompat.Builder(context);
       builder.setSmallIcon(R.drawable.icon_notification);
-      builder.setContentTitle("Import Complete");
-      builder.setContentText("TextSecure system database import is complete.");
+      builder.setContentTitle(context.getString(R.string.ApplicationMigrationService_import_complete));
+      builder.setContentText(context.getString(R.string.ApplicationMigrationService_Signal_system_database_import_is_complete));
       builder.setContentIntent(PendingIntent.getActivity(context, 0, new Intent(context, ConversationListActivity.class), 0));
       builder.setWhen(System.currentTimeMillis());
       builder.setDefaults(Notification.DEFAULT_VIBRATE);