Capture original file size

This addresses #356 although not ideally. The issue is that the uploaded file is converted to png, which if there source is jpeg, can result in a file that is larger than the original.  The validate was checking against the size of the converted file, which was larger than the original.

After digging around CarrierWave, the best solution I could come up with was to grab the original file size and and check it afterwards.  Suggestions? @jcoyne @mjgiarlo