[CleanRepo] Orphaned images being mistakenly removed

[davidbritch]

While using cleanrepo to remove orphaned images on xamarin-docs-pr I discovered the following markdown formats weren't being handled by the tool, and so images were being removed that shouldn't have been:

    ![The Widget tab for an activity
    indicator](progress-indicators-images/activity02.png "The Widget tab for
    an activity indicator")

A high resolution version of the class diagram can be downloaded from [here](class-hierarchy-images/class-diagram-high-resolution.png).

I particularly like the multiple cases of spreading an image link over three lines! Not sure if it's worth the tool handling this. I just fixed the markdown instead. But there were quite a few examples of the second case where an image is actually a download link. In those cases I dropped the images back in place after they were removed. There was also a third case due to writer error on lightbox images (where the images actually rendered fine on learn, despite the markdown being incorrect) - I fixed those.