While clicking on redlinks in source article, make the link red

The source article shows blue links for all kind of links. But it is when
user click on a source link, we get to know whether it is a redlink.
Mark it as redlink by adding a class redlink.

Ideally, we need to identify red links when page is loaded, but that is
bit complicated and involves API hit etc.

This solution seems to be 'better than nothing' approach.

Source link card does not appear when clicking on such links.

Change-Id: I7aa777e2bbabad76e068d0991bb185d5615786e2
Merge "While clicking on redlinks in source article, make the link red"