app: sequence management -- new-sequence dialog, folders, sequences in the project bin

- File > New > Sequence opens a real dialog (name, PAL/NTSC/HD presets,
  width/height/frame rate, progressive/interlaced); VideoParams gains an
  interlaced flag
- File > New > Folder creates a folder in the project root
- sequences are mounted under the root folder so they appear in the
  project explorer (including the auto-created Sequence 1 and orphans
  from older projects); right-click > Sequence Properties edits the
  parameters afterwards
- dropping footage onto an empty, sequence-less timeline auto-creates a
  sequence from the footage's first video stream

crates/oak-node/src/footage.rs

@@ -438,6 +438,10 @@ impl NodeBehavior for FootageBehavior {
 					writer.attribute("framerate", &v.frame_rate.to_display_string());
 					writer.attribute("pixelformat", &v.pixel_format.to_string());
 					writer.attribute("channels", &v.channels.to_string());
+					writer.attribute(
+						"interlaced",
+						if v.interlaced { "1" } else { "0" },
+					);
 					writer.end_element(); // video
 				}
 				if let Some(a) = s.audio {
@@ -586,6 +590,10 @@ impl NodeBehavior for FootageBehavior {
 												.attribute("channels")
 												.and_then(|v| v.parse().ok())
 												.unwrap_or(0),
+											interlaced: reader
+												.attribute("interlaced")
+												.map(|v| v == "1")
+												.unwrap_or(false),
 										});
 										// Consume the (self-closing) element.
 										let _ = reader.read_element_text();
@@ -673,6 +681,7 @@ fn streams_from_description(
 				frame_rate: oak_core::Rational::new(num as i64, den as i64),
 				pixel_format: vp.format().code(),
 				channels: vp.channel_count(),
+				interlaced: false,
 			}),
 			audio: None,
 			duration: stream_duration_seconds(vp.duration(), vp.time_base()),

crates/oak-node/src/sequence.rs

@@ -138,6 +138,7 @@ impl SequenceBehavior {
 			frame_rate: oak_core::Rational::new(fps_num as i64, fps_den as i64),
 			pixel_format: 4, // f32
 			channels: 4,
+			interlaced: false,
 		}];
 		self.audio_params = vec![AudioParams {
 			sample_rate,

crates/oak-node/src/value.rs

@@ -580,6 +580,8 @@ pub struct VideoParams {
 	pub pixel_format: i32,
 	/// Channel count.
 	pub channels: i32,
+	/// Whether the stream is interlaced.
+	pub interlaced: bool,
 }
 
 /// Audio parameters (plain data).