various: allow users to override the start and end index of image sequences

Also includes various fixes to footage property setting/signalling.

app/render/backend/videorenderworker.cpp

@@ -179,6 +179,8 @@ void VideoRenderWorker::HashNodeRecursively(QCryptographicHash *hash, const Node
             if (stream->type() == Stream::kVideo) {
               hash->addData(QStringLiteral("%1/%2").arg(QString::number(input_time.numerator()),
                                                         QString::number(input_time.denominator())).toUtf8());
+
+              hash->addData(QString::number(static_cast<VideoStream*>(stream.get())->start_time()).toUtf8());
               /*Decoder::RetrieveState state = decoder->GetRetrieveState(input_time);
 
               if (state == Decoder::kReady) {