add start_id and end_id to .../recordings json

This was added to the API documentation in eee887b9 but never actually
implemented then. It's necessary to actually fetch the .mp4 in question.

src/json.rs

@@ -125,7 +125,11 @@ pub struct Recording {
     pub end_time_90k: i64,
     pub sample_file_bytes: i64,
     pub video_samples: i64,
+    pub video_sample_entry_sha1: String,
+    pub start_id: i32,
+
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub end_id: Option<i32>,
     pub video_sample_entry_width: u16,
     pub video_sample_entry_height: u16,
-    pub video_sample_entry_sha1: String,
 }

src/web.rs

@@ -427,7 +427,9 @@ impl Service {
                            .ok_or_else(|| Error::new("no such camera".to_owned()))?;
             db.list_aggregated_recordings(camera.id, r, recording::Duration(i64::max_value()),
                                           |row| {
-                out.recordings.push(json::Recording{
+                out.recordings.push(json::Recording {
+                    start_id: row.ids.start,
+                    end_id: if row.ids.end == row.ids.start + 1 { None } else { Some(row.ids.end) },
                     start_time_90k: row.time.start.0,
                     end_time_90k: row.time.end.0,
                     sample_file_bytes: row.sample_file_bytes,