MOV file video support

[j-te]

Hello! First of all thanks to everyone involved in maintaining this project.

1. There seems to be an issue with displaying MOV files (I believe they're not a default supported filetype). It should be an easy one to add playback support using a video and source tag.
2. File previews (image and video) currently do not display well in the browser. There are container scaling issues.
3. I believe we can expand on the file preview logic to insert custom html using templates, this would be a powerful feature. We need support of custom attributes for controlling encoding etc.

I understand that the above can be resolved with custom forms but I believe we should make improvements to the out-the-box support of file previewing. I may be able to support here but wanted to start a discussion as I'm new to this project/there are probably project milestones I'm unaware of.