Fix toot postion on big screen navigatin with j / k

[Marzal]

Is your feature request related to a problem? Please describe.
On Desktop next toot changes up and down navigating with the keyboard shortcuts

Describe the solution you'd like
Next toot selected is either at the top or at the same vertical height

Describe alternatives you've considered
Top seems easy, but the center of the screen would be great.

Additional context
#246 (comment)

Thanks for this amazing client.

[jan-vandenberg]

Yes this! The j/k navigation is good, but it needs to always display the selected toot at the top. Just like Twitter.
Because toots are different sizes navigation is yanky and your eyes have to keep scanning where the next toot will end up. If the toot in focus is always at the top, that would make for a much better experience!