refactor(task): OTIO load/save tasks over oaknode/oaktimeline C ABIs

- LoadOTIOTask/SaveOTIOTask de-Qt'd: graph traversal and construction
  through oaknode C ABI (find_input_footage, sequence defaults, block
  factories, context positions), track creation through oaktimeline's
  add_track command; the OTIO import dialog becomes a facade callback
  (headless default: accept all)
- oaknode additions: find_input_footage, sequence_set_default_parameters
- USE_OTIO + otio-install libs wired into oaktask; OTIO dylibs copied
  next to liboaktask for @loader_path resolution
- OTIO round-trip test passes; build-oaktask 106/106 green

include/node/sequence.h

@@ -83,6 +83,12 @@ void oaknode_sequence_free(OakNodeSequence *sequence);
  * @param type One of OAKNODE_TRACK_TYPE_VIDEO / _AUDIO / _SUBTITLE.
  * @return OAKNODE_OK, OAKNODE_E_INVALID or OAKNODE_E_NOT_FOUND (bad type).
  */
+/**
+ * @brief Apply the default video/audio parameters
+ *        (ViewerOutput::set_default_parameters()).
+ */
+int oaknode_sequence_set_default_parameters(OakNodeSequence *sequence);
+
 /**
  * @brief Borrowed cast from a sequence handle to its node handle.
  * NULL for NULL.