simplify code for presenting list of available image sets

[brobertson]

This is a 5x speedup:

for $imageset in //lace:imagecollection
    let $text := $imageset/dc:identifier
    order by $imageset/dc:creator[0]
    return 
        if (exists(//lace:run[dc:identifier = $text]))
        then
            <yes>{$text}</yes>
        else 
           <no>{$text}</no>

[brobertson]

fix also app:countCatalog and app:get-lace-version

[brobertson]

in general, check for 'collection('/db/apps')' because this is something that really drags things down.