Reworked shortcuts / next & previous

- next and previous shortcut now toggle story
- when a story is toggled, screen is scrolled
- added b as a shortcut to open permalink to match Reeder shortcuts
- permalink now targets _blank
Made links open in background tab

Got to pack some OS detection for guessing ctrl/cmd key
Removed meta key trick to open in bg

Permalink has no target (html)
When key [b] or [v] is pressed, it opens in a new window (tab) in
foreground.
fix css issues caused by feed/story list borders.
small tweaks. dont toggle stories at the ends.
Merge branch 'pr/44'