Generate file previews

[aonnikov]

For files that cannot be shown right away we need to generate previews and show them where needed.

Preview libraries to consider:

• https://github.com/fluent-ffmpeg/node-fluent-ffmpeg
• https://www.npmjs.com/package/psd
• https://github.com/webtoon/psd

_{Huly®: UBERF-7355}