Add scrolling through posts via volume keys. Closes #209

[eugenkiss]

I like the effect very much! Good work :+1:

Can I add an additional request? Namely, if you switch from portrait to landscape and then scroll via volume keys the distance is too great because it is still based on portrait. The fix is to recalculate SCROLL_BY_HEIGHT in the postDelayed-callback of PostsActivitys onConfigurationChanged method.

[eugenkiss]

Oh and another issue, if you have a PostsDialog open (i.e. you clicked on Replies) then the volume key scrolling scrolls the main thread behind but not the current PostsDialog at the top.

[wadlieb]

I will fix the PostsDialog issue next :smiley:

[eugenkiss]

Good job!