unittest ddrimport with CSV files and binaries

[gjost]

Make CSVs with representative entity/segment and file content including binaries.

Make tests that

• [x] create a collection repo
• [x] ddrimport create entities/segments
• [x] ddrimport update entities/segments
• [x] ddrimport create files
• [x] ddrimport update files

Import/update various file types:

• [x] local binaries (actual file imports)
• [x] external binaries (file lives in Internet Archive)
• [x] ???

Generate access files

[gjost]

Basic testing done in ddr-cmdln commit 78d4b95.