finalized very, very basic OTIO support

Ironed out various project and footage loading issues, and a single
cache invalidation issue.

app/project/item/footage/footage.cpp

@@ -308,7 +308,7 @@ bool Footage::CompareFootageToItsFilename(FootagePtr footage)
     } else {
       // Footage may have changed and we'll have to re-probe it. It also may not have, in which
       // case nothing needs to change.
-      ItemPtr item = Decoder::ProbeMedia(footage->filename(), nullptr);
+      ItemPtr item = Decoder::ProbeMedia(footage->project(), footage->filename(), nullptr);
 
       if (item && item->type() == footage->type()) {
         // Item is the same type, that's a good sign. Let's look for any differences.

app/project/item/sequence/sequence.cpp

@@ -151,7 +151,7 @@ void Sequence::Load(QXmlStreamReader *reader, XMLNodeData& xml_node_data, const
 
   // Ensure this and all children are in the main thread
   // NOTE: It might be good to move the Item system to QObjects so they inherit their thread
-  if (thread() != qApp->thread()) {
+  if (QThread::currentThread() != qApp->thread()) {
     moveToThread(qApp->thread());
   }
 }