cleanups for DownloadAuth

remove unused session variable, div id quoted, better conditional
statements
test correct timed eviction in TimedEvictingQueue
use ms to measure period for downloads
fix log message for download count
label with instructions for captcha
renewing challenge (captcha) by attaching milli parameter
better handling of maxAggregatedDownloadsPeriod, now used as minutes in config
register gogoduck downloads only if successful