Prevent duplicate crawls in CrawlManager
if endpoint/datamodel combo already waiting or processed, skip further scheduling
(from redmine: issue id 945, created on 2018-01-29tgradl, closed on 2018-02-09)
if endpoint/datamodel combo already waiting or processed, skip further scheduling
(from redmine: issue id 945, created on 2018-01-29tgradl, closed on 2018-02-09)