Add "remove podcast" in toolbar and "Downloaded podcasts" special folder

[mkanilsson]

This PR adds 1. a trashcan icon in the toolbar when in a podcast and 2. a special Downloaded Podcasts in the sidebar.

This is a draft because:

1. The UI doesn't update and adds the trashcan icon when a podcast has been downloaded.
2. I can't manage to get the number of downloaded podcasts to show up in the sidebar.

NOTE: This is a breaking change which makes users unable to play their already downloaded podcasts, the reasons for this is: Before, the media was stored in md5_hashed_url/filename but since sqlite doesn't have a MD5 function I had to change the path to rss_item_fingerprint/filename so I can use a fingerprint in (ids) query and get all downloaded podcasts

Once this is done, it will close #742

podcast.mp4

[David-Development]

Wow! This is an awesome feature! I really like the idea of having a "folder" for all podcasts that are downloaded. Makes it much easier to keep track of them. Just a quick thought.. we need to make sure to keep articles with downloaded items around - even if they're marked as read. Otherwise they might be removed from the phones database (ref) in case the user has many unread articles. I'll try to do an more in depth review today/tomorrow!

[mkanilsson]

@r3tr0-git It's done, it just needs to be reviewed (and maybe changed depending on how the review goes of course).

[David-Development]

@mkanilsson Sorry - I think you have a few conflicts now since I did some refactoring in the sidebar. Once everything looks good from your side you can mark it as "Ready for review". Currently it's still marked as "Draft".

[mkanilsson]

I'm very sorry for the delay, I got a new job so I've been quite busy.

Everything should be fixed now and should be able to merge cleanly.

Hmm, it complains that all commits must be signed, which they are...

[David-Development]

@mkanilsson No worries, thank you for finishing this MR! And congrats to your new job!

Looks great to me - I just noticed that there are a few strings that are not translated yet - I'll merge it already and add them as translations in a separate MR.