whitespace cleanup
 - adds "ngaid" attr to the shortcode to display NextGen Albums
 - adds post_gallery filter to enable [gallery photomosaic="true"]
 - updates post_gallery filter to allow [gallery template="photomosaic"]
 - adds 'template' option to 'Gallery Create' flow
 - adds 'thumbnail' to WP sizes
Bug Fix: images that return a 404 are now removed from the gallery
 - Enhancement: input:html now pulls image dimension (height/width) info from node attrs
 - Refactor: Error Checks have been moved to the same place