various: allow setting footage aspect ratios

We had support for detecting aspect ratios and respecting them in the
render, but this allows people to not only see the aspect ratio in use,
but also override it with their own.

app/codec/oiio/oiiodecoder.cpp

@@ -119,6 +119,9 @@ bool OIIODecoder::Probe(Footage *f, const QAtomicInt *cancelled)
   image_stream->set_height(in->spec().height);
   image_stream->set_format(GetFormatFromOIIOBasetype(in->spec()));
 
+  // FIXME: Haven't looked, does OIIO report pixel aspect ratio somewhere?
+  image_stream->set_pixel_aspect_ratio(1);
+
   // Images will always have just one stream
   image_stream->set_index(0);