media progress

### Your use case

Currently on holiday seeing family members using Element and also WhatsApp and hearing the complaints about Element. Tested with the `0.6.2` release.

#### What would you like to do?

Very noticeable on slower connections is that you can't see where media download is.

#### How would you like to achieve it?

Add a download progress bar from 0 to 100 or circle that shows the real progress.

### Have you considered any alternatives?

No

### Additional context

Now with images you see a placeholder but you don't see the size or the progress of loading the media. They feel it is slow.

For videos you see a generic loading animation but it doesn't give you any idea how long you need to wait for the video to be loaded.

### Are you willing to provide a PR?

No