Externalize MFR

Purpose
-----------
Current implementation of the modular file renderer is not very modular. Making the MFR its own project increases modularity. New MFR functionality is greater than or equal to functionality of the old MFR.

Changes
------------
* Externalize MFR
* Improve support for .pdb by switching rendering libraries
* Improve support for audio files
* Improve support for tabular files
* Add (browser dependent) support for ogv/webm/mp4 video files

Side Effects
----------------
Miscellaneous other bug fixes, see MFR's [commit log](https://github.com/CenterForOpenScience/modular-file-renderer/commits/dev) for details.