Support custom image upload backgrounds for individual audiograms about audiogram

[veproza]

If anyone would be interested, I added this functionality to our app with this commit: DataRozhlas@921ebd6. If you'd like, I can make it into a pull request, or feel free to cherry-pick it.

It works that it draws either the uploaded image, the theme image or no image, in this order. The biggest change was the need to handle upload of multiple files, hence the renaming of req.file to req.file.audio.

[korymath]

Currently it would be a matter of modifying the themes.json right?

[veltman]

This is about letting people upload images for individual audiograms, not for an entire theme (e.g. uploading a photo of the person who's being interviewed in a particular clip).

We haven't prioritized this so far because it would require a whole interface for moving/stretching/position each image and quality control is hard - opening up image uploading like that means it's easy for people to put in photos that look bad or they don't have the rights to.

[veltman]

Closing in favor of #32.