Add `column_order` display option for columns and foreign keys [ci skip]
Add `column_order` display option for columns and foreign keys [ci skip]

- Reuses the same sort-key syntax as table row_order
- Extends 2016 Column Display w/ another contextualized option
- Extends 2016 Foreign Key with a contextualized `display` option section
- Describes heuristics and caveats for supporting semantic sort

informatics-isi-edu/ermrest,informatics-isi-edu/ermrest