Bug Fix: fallback image alignment for video expandos

Video expandos for imgur, gifyoutube, and possibly others cause alignment issues when a relevant mp4 or webm video is not found and instead it falls back to the original image. since the <img> tage in the fallback logic was missing class definition, some browsers would shove the image to the right. Setting the RESImage class for the fallback image ensures the <img> tag is identical to the tags for normal images.

reported: https://www.reddit.com/r/RESissues/comments/2jmzuc/bug_inline_gifs_jump_over_after_they_load/