Added ability to select which fields to return, instead of always returning all fields.
Added support for :distinct to application controller.  User can now specify a
column and only get back rows with distinct values of that column.
Added 'select' and 'distinct' parameters to discovery document.  Improved
select parameter to parse strings as json.
Merge remote-tracking branch 'origin/master' into 2035-arv-mount-tags-folders

Conflicts:
	services/api/app/controllers/application_controller.rb
Fix for interaction between 'select' and 'order' (SQL requires that order
fields show up in select when doing select distinct; readable_by does 'select distinct' by default to avoid duplicate rows).
Fixed botched 'distinct' parameter, now is a boolean instead of taking a
column.  New tests.  Also changed syntax of 'order' to take a JSON array for
consistency with 'filters' and 'select'.
Restored support for old-style 'order' strings and added test.  Clarified
documentation for 'distinct' as to the default behavior.
Merge branch 'query-select-distinct'