Make sure that the browser doesn't follow links while in click/hide mode

Review: http://codereview.adblockplus.org/4998212691689472/
Click-hide: if the current element cannot be blocked, select its parent

Review: http://codereview.adblockplus.org/4998212691689472/
Click-hide: React to Enter and Escape keys rather than the obscure Ctrl-Shift-E hotkey

Review: http://codereview.adblockplus.org/4998212691689472/