(bug 24437) Add nofollow to image link

(bug 24437) Add nofollow to image link

Add Parser's extLinkAttribs attributes when an image has a link
parameter, when generating the html. Currently, these may include
rel="nofollow" and the target attribute.

This will correctly add rel="nofollow", respecting $wgNoFollowLinks,
$wgNoFollowDomainExceptions, and $wgNoFollowNsExceptions settings.

Updated parser tests for expected results, added new tests for
$wgNoFollowLinks and $wgNoFollowDomainExceptions exceptions.

Change-Id: Ib4677760ec78a3f0c4ba781d893e0484cc8db3ed