Add quick download button

[iamntz]

Deals with #720

[kieraneglin]

Hey there! Thanks for the contribution (:

I just tried this out locally and I think there are a few things that need addressing:

• The button should only show up for videos in the Other tab (and maybe the Pending tab, but I'm unsure there. It seems like a confusing use-case since pending is meant for content that is intended to be downloaded). There are examples in the file like the one for Manually Ignored? that uses a conditional check for @media_state == "other"
• More pressing, I don't think opening this link in a new page is the right call. Ideally, phx-click could be used along with a handle_event to run the logic without requiring a redirect/page load

Please let me know if you want to take this on and if you have any questions!

[iamntz]

since pending is meant for content that is intended to be downloaded

Actually, from the way I use it, pending seems to be more like „the content that is not downloaded yet”. Which sounds the same, but it kind of isn't.

As I mentioned, while you just „watch” a channel for new videos (but without automatically download anything), any videos that are not downloaded are showing up in pending tab.

I've pushed a fix that will hide the button on downloads tab. (though I think that we should display a _re_download button on downloaded tabs?)

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I don't know how phx-click should work, as I'm not familiar with elixir and/or phoenix 🥲.

Will dig a bit to see how it may work.

Pushed a fix:

1. it replaces the download link with button_icon (it makes more sense this way)
2. added the buttons on homepage's pending tabs as well
3. the download will trigger in-place loads, without any new tabs or reloads
4. tweaked the spacing on the item row

I guess that's pretty much it, as I don't know if there is a way to display a success message in place (but if would be: maybe make the button change icon? maybe change its color?)