File repo frontend: 1) file browser, 2) file renderers
DM4 had a file repo service in the backend, and a frontend for 1) browsing the file repo, and 2) file renderers for PDF, Images, Audio, Video. In DMX the FilesService
backend is still there, but the frontend features are missing. These shhould be implemented in DMX Webclient as well.
This is a follow-up of dmx-intern/sprint-planning#40
See also dmx-intern/sprint-planning#218