Have parser check for the existence of appendix image thumbnails for display in reg text

Some appendices crash the browser under certain circumstances because, even with lazy loading, there are simply too many large images loading. This is part #2/3 of new functionality to have smaller (max 400px width) images display inline in reg text, with the full size being available by clicking on the image.

For the CFPB-hosted instance of eRegs, I've created thumbs for everything in eregsip. When thumbs aren't available, the full size is used.