Add more attachment support

[mantycore]

• [ ] Support for GIF, WebG, SVG (and animation? Animation could be stopped)
• [ ] Dowloading of any files
• [ ] Players for audio and video files
• [ ] Text preview for text files? (possibly including rtf, doc, etc)

[0x1a1a1a]

I think that it would be better to split this issue on 4 different issues, move to "Ideas Inbox" for now as not essential and reprioritize later.