Add ability to save media

[sk4k2k]

Please add a way to save images, videos, GIFs or other media to the client's device.

[aeharding]

Thanks for the issue.

Would be best as an ellipse in the media viewer, like apollo.

[tomtclai]

On Apollo we can tap and hold on the image viewer to save photo

[Penagwin]

@aeharding I think my PR #226 addresses the images if you wanted to merge that now.

I think saving videos might require a few extra steps, I need to test it some more but I don't think -webkit-touch-callout:default; alone works on the videos.

[aeharding]

There's perhaps more we could do here in addition to the above, but it would best if this was actionable work in a new issue. Closing this one :)