Find images also when file name is missing extension

[ktraunmueller]

If the image file name in an \includegraphics is missing an extension, Compositor will currently fail to load find the image. It would be nice if the app would be a bit smarter (detect missing extension, try the most common ones) here.

Example: the ASA's POMA template: https://asa.scitation.org/pma/authors/manuscript