Since user can choose imagecache preset for thumbnails their width and height should not be hardcodedt

when using custom imagefield presets the gap between image/imagethumbs/prev-next-buttons can either be too much or too little

this patch gets rid of width and height from galleria.css

width:80px;
height:80px;
margin:10px 10px 0 0;

margin is changed to what I believe to be a more sensible default (irrelevant of the previous change)