Pause Heritrix jobs when validation queue is too large

[yuliya-ivaniukovich]

For some domains we obtain a large amount of downloaded pdf files which are placed in validation queue. Maybe we have to make some heritrix pausing mechanism? If we have already more than X files for this domain in queue, then pause heritrix crawling for this domain and resume it after the amount of files in queue will become less than Y (this is server machine storage optimization)