Playlists Browser: enable searching of contents

[declension]

@lazka - as discussed really. Please have a look, we can either then merge or update first.

• Add searchbar as per other browsers, mostly.
• Query is normal QL syntax
• Searches persist across playlists selection
• Text-compatible filtering supported too (TODO: ~playlists tag should select playlist)

Closes #1588.

[declension]

@lazka - Thanks.

Weird, I can't replicate that UI behaviour; the queue stays shut for me, and if I don't show the songpane, I don't get a songpane at all it seems.

As for the active_filter()... I see. Is it in fact possible to remove it here entirely, as newly added songs will never be auto-added to a playlist (well, not without a whole lot new work)? That said, songs removed from the library should get removed from the songlist I guess, and it seems safer to implement it as a filter on both active playlist and text filter... so maybe I'll do that.

[lazka]

I mean if you hide the queue completely, not just close the expander.

for active_filter(), removals are still handled in the song list directly atm, so you can probably just remove it for now.

[declension]

Oh, right, I forgot you could even do that (again...)!

I've fixed that behaviour in the packing (AFAICT), and as for the active_filter, made it consistent with the others for now.

Perhaps we can think about cleaning that interface up at some point? IMO it feels a bit inconsistent with the rest of the Browser interface, or something.

[declension]

@lazka - are you happy for me to merge the updated version?