improve link detection in notify-link-clicks
improve link detection in notify-link-clicks

Original approach is a bit too naive and misses all links
that contain other elements which can grab mouse clicks.
E. g. simple target checking fails on the grid @ mozilla.org.

Traversing up the tree to look for valid links fixes this problem.

andymckay/webextensions-examples,mdn/webextensions-examples,evolighting/webextensions-examples,mdn/webextensions-examples,evolighting/webextensions-examples,anaran/webextensions-examples,anaran/webextensions-examples,mdn/webextensions-examples,matthewjwein/webextensions-examples,matthewjwein/webextensions-examples,matthewjwein/webextensions-examples,evolighting/webextensions-examples,andymckay/webextensions-examples