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/decoder.h

@@ -138,7 +138,7 @@ public:
    * A FramePtr of valid data at this timecode or nullptr if there was nothing to retrieve at the provided timecode or
    * the media could not be opened.
    */
-  virtual FramePtr RetrieveVideo(const rational& timecode, const int& divider, bool use_proxies);
+  virtual FramePtr RetrieveVideo(const rational& timecode, const int& divider);
 
   /**
    * @brief Retrieve video frame
@@ -210,11 +210,6 @@ public:
    */
   static DecoderPtr CreateFromID(const QString& id);
 
-  /**
-   * @brief VIDEO ONLY: Produce a compressed EXR proxy with the specified divider
-   */
-  virtual bool ProxyVideo(const QAtomicInt* cancelled, int divider);
-
   /**
    * @brief AUDIO ONLY: Produces a complete PCM extraction of the audio stream
    *