Patch that allows images also to be specified by name rather than path

Issue Summary

This is a great module, but end users of my site will find it difficult to figure out how to enter paths to the images they want to appear in their image menus, so I created this patch that allows them to enter the name of the image, which is then looked up to provide the full path to imagemenu. If an image cannot be found by name, then the input is treated as a full path (as before).

Another improvement to this excellent module might be to have AJAX auto-complete fields for the images on the setting form - this will make it even easier for users to choose images.

Thank you,

Nick