Externalize MFR

Purpose
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Current implementation of the modular file renderer is not very modular. Making the MFR its own project increases modularity. New MFR functionality is at least equal to functionality of the old MFR.

Changes
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* Externalize MFR
* Increase support for .pdb by switching rendering libraries
* Increase support for audio files
* Add (browser dependent) support for ogv/webm/mp4 video files

Side Effects
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* Update PyDocx supported version
* Fix other bugs