Add untagged support.

[mathwhiz1212]

I am transitioning over from pocket and I am used to have a sort by untagged option and I would really appricate it if you added it in a later version. I don't think it would be that hard you could just add it to the tags. If I am missing something that is already in wallabag (v.1.8.1) that does the same thing please let me know.

[tcitworld]

You mean, get all the article which aren't tagged ?

[mathwhiz1212]

Yes, it would (in theory) act pretty much like a tag, that way the ones I have already sorted aren't in my way when I'm trying to sort the untagged articles which makes it a lot easier to deal with 1,000+ articles.

[tcitworld]

Will try some things, without promise it will done soon, since it must be much easier to deal with that kind of feature on v2.

[j0k3r]

Duplicate of #1631