Feature/multi run

[jbrown-xentity]

Related to GSA/data.gov#3527, optimization and cleanup. This adds 2 optimizations:

• Allows to hit a read-only url for read api calls (defaults to same as api-url, which defaults to read-write catalog URL)
• Sorts the duplicate identifier list by default, and adds a flag to reverse the sort. This allows to run 2 scripts in parallel, which cuts total run time by about 40% (not quite 50%, running 2 at the same time slows down queries a bit on the catalog).

It also simplifies the API call to get the duplicate identifiers.
Does some tiny cleanup for GSA/data.gov#2744