implemented raw file type handling

I made a small improvement to make cloudinary raw/non-image files possible.

has_attachment :video, accept: [:raw, :mpg, :mpeg, :mp4]

Will make .mpg .mpeg and .mp4 files possible. Because raw files do not have thumbnails a placeholder div is gonna be added to the widget that can be customized with css.

The only downside is, that in this case also .raw files could be uploaded. I haven't figured out a way to solve this.