Feature: select single channel

[oldnomad]

Description of the issue

It seems that with the latest rewrite, OCReader has lost an ability to select articles from single channel. In versions up to 0.44 a swipe from the right edge showed a list of channels, from which I could select one to view only articles from this channel. In 0.45 I see only folders, there's no way to select single channel.

Expected behavior

A method to select articles from a single channel.