decoder/renderer: no longer index automatically as part of the retrieve

functions

Indexing is a lengthy process and had a high chance of getting RenderWorkers
stuck doing it rather than being responsive to cache requests. This commit
introduces a system where workers never index media, but instead signal that
media is not ready to their RenderBackends which ensure that the media gets
indexed and re-queues the affected frames when those indexes are ready.

app/common/timerange.h

@@ -33,6 +33,8 @@ private:
 
 };
 
+Q_DECLARE_METATYPE(TimeRange)
+
 uint qHash(const TimeRange& r, uint seed);
 
 class TimeRangeList : public QList<TimeRange> {