Issue title: Have each folder bahaving as the main page
 Issue body: When we are on the main page, clicking 'read' for an article makes it disapear from the list.
this would be great if the same behavior could happen when selecting a given directory.

 Comments: 
 Comment 0: use the shortcut key "M" to mark the item as read and move to the next automatically.

 Comment 1: Indeed, 'M' mark the item as read but doesn't move to the next one. The idea behind the request was more to be able to read some items the same way as the main page for a given category. The reason is that for instance if I have a folder news with several newspaper feeds, the frequency of update is higher for this one, and at the end I end up reading lots of news while other topics are left behind because I really like the behavior of the main page. That's just a nice to have suggestion. This rss reader is for me the best I have tried at this moment.

 Comment 2: @lolovroom : So, if your suggestion is implemented, where will you read _all_ the articles in a given category ? You'll have to refresh the page much more often. I personnally think the actual behaviour is much more logical than this one, as a category has a certain amount of feeds that should always be there and readable.

{'source': 'GithubIssues', 'repo_name_with_owner': 'LeedRSS/Leed', 'issue_id': 12619772, 'repo_stars': 188.0}