Fix scrolling with new browser in Unified layout
Fix scrolling with new browser in Unified layout

Contrarily to UIKit, AppKit does not implement the scrollView property
for WKWebView, so this is the only solution I found for customizing
the scrolling behavior. 
ViennaRSS/vienna-rss,ViennaRSS/vienna-rss,ViennaRSS/vienna-rss,josh64x2/vienna-rss,ViennaRSS/vienna-rss,barijaona/vienna-rss,josh64x2/vienna-rss,barijaona/vienna-rss,ViennaRSS/vienna-rss,josh64x2/vienna-rss,barijaona/vienna-rss,josh64x2/vienna-rss,barijaona/vienna-rss,barijaona/vienna-rss,josh64x2/vienna-rss