various: implement sequence pixel aspect ratios and interlacing settings

Implements the following:
- Sequences have pixel aspect ratios that work in tandem with footage PARs
  to render footage correctly. Viewer and export also acknowledge PARs
- Sequences can have interlacing settings. This doesn't do anything yet,
  eventually the renderer will need to interlace/deinterlace/reinterlace
  appropriately in order to conform all the footage to the sequence. Export
  acknowledges interlacing, but this only affects metadata, not the image.

app/codec/frame.cpp

@@ -27,8 +27,7 @@
 OLIVE_NAMESPACE_ENTER
 
 Frame::Frame() :
-  timestamp_(0),
-  sample_aspect_ratio_(1)
+  timestamp_(0)
 {
 }
 
@@ -106,20 +105,6 @@ void Frame::set_pixel(int x, int y, const Color &c)
   c.toData(data_.data() + byte_offset, video_params().format());
 }
 
-const rational &Frame::sample_aspect_ratio() const
-{
-  return sample_aspect_ratio_;
-}
-
-void Frame::set_sample_aspect_ratio(const rational &aspect_ratio)
-{
-  if (aspect_ratio.isNull()) {
-    sample_aspect_ratio_ = 1;
-  } else {
-    sample_aspect_ratio_ = aspect_ratio;
-  }
-}
-
 const rational &Frame::timestamp() const
 {
   return timestamp_;