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/render/backend/renderbackend.h

@@ -62,6 +62,8 @@ public:
 
   void ClearVideoQueue();
 
+  void ProcessUpdateQueue();
+
   /**
    * @brief Asynchronously generate a hash at a given time
    */
@@ -98,8 +100,6 @@ private:
 
   void RunNextJob();
 
-  void ProcessUpdateQueue();
-
   ViewerOutput* viewer_node_;
 
   // VIDEO MEMBERS