project: replaced proxy with pre-cache

Removed proxy task and replaced with a true honest-to-god pre-cache for
footage. This footage is pre-cached to a sequence and therefore 100% ready
for use in it once the task is done.

app/codec/oiio/oiiodecoder.cpp

@@ -154,7 +154,7 @@ bool OIIODecoder::Open()
   return true;
 }
 
-FramePtr OIIODecoder::RetrieveVideo(const rational &timecode, const int& divider, bool /*use_proxies*/)
+FramePtr OIIODecoder::RetrieveVideo(const rational &timecode, const int& divider)
 {
   QMutexLocker locker(&mutex_);