Be able to render mp4 and mp3 files

[hunterlester]

When navigating to html, jpg, or png file in address bar, browser renders them in webview accordingly.
In Beaker I was able to navigate to an mp4 or mp3 file and it would be rendered accordingly, however, SAFE Browser is not currently replicating this behavior.

[bochaco]

I asked @joshuef some days ago about rendering PDFs and he pointed out this: https://stackoverflow.com/questions/43220321/electron-pdf-viewer, perhaps it's the same solution for all type of formats. I'd love to have all these formats supported by the browser.