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/task/proxy/proxy.h

@@ -1,46 +0,0 @@
-/***
-
-  Olive - Non-Linear Video Editor
-  Copyright (C) 2019 Olive Team
-
-  This program is free software: you can redistribute it and/or modify
-  it under the terms of the GNU General Public License as published by
-  the Free Software Foundation, either version 3 of the License, or
-  (at your option) any later version.
-
-  This program is distributed in the hope that it will be useful,
-  but WITHOUT ANY WARRANTY; without even the implied warranty of
-  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-  GNU General Public License for more details.
-
-  You should have received a copy of the GNU General Public License
-  along with this program.  If not, see <http://www.gnu.org/licenses/>.
-
-***/
-
-#ifndef PROXYTASK_H
-#define PROXYTASK_H
-
-#include "project/item/footage/videostream.h"
-#include "task/task.h"
-
-OLIVE_NAMESPACE_ENTER
-
-class ProxyTask : public Task
-{
-public:
-  ProxyTask(VideoStreamPtr stream, int divider);
-
-public slots:
-  virtual bool Run() override;
-
-private:
-  VideoStreamPtr stream_;
-
-  int divider_;
-
-};
-
-OLIVE_NAMESPACE_EXIT
-
-#endif // PROXYTASK_H