Add a shortcut for jumping to the next category with unread entries

[parnic]

Is your feature request related to a problem? Please describe.
It would be nice if I was able to jump to the next unread category with Shift+J so that I can read through everything using only the keyboard when viewing entries outside of "All" mode. (Feedly supports this.)

Describe the solution you'd like
When I am viewing a category and press Shift+J, the next category with unread entries is selected and shown. If there are no remaining unread entries, nothing happens.

If I am viewing a specific feed, the next feed with unread entries should be selected instead of the next category.

Describe alternatives you've considered
Clicking with the mouse.

Additional context
This mirrors a Feedly feature. Shift+K should probably do the same thing, but for the previous category.

[doowruc]

Additionally, it would be good if:

J jumps to next unread in the next feed when on last article in a feed

Mark all as read also jumps to next feed with unread

[tomhusband]

Has this been clarified? I'd like to see this feature too.

[Athou]

I added the shift+j and shift+k shortcuts, it will be part of the next release.

J jumps to next unread in the next feed when on last article in a feed

I'm not sure I like this, you could lose the list of current entries by pressing J one time too many by mistake. I prefer the solution proposed by @parnic which is a dedicated shortcut to navigate to another feed/category.

Mark all as read also jumps to next feed with unread

When marking all as read, the current behavior is to reload the current feed/category because there may be new entries that were fetched by the server but not yet shown in the client.