clarify sorting order annotations and add explicit disable syntax
clarify sorting order annotations and add explicit disable syntax

- `"column_order": false` can disable sorting by foreign key or column
- be explicit that some column types may not be sortable
- heuristics can recursively walk the model
    - foreign key can obey row_order of referenced table
    - non-composite foreign key can follow consituent column rules
    - consituent column can follow column rules of referenced table column

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