3412: Clean API Collections controller trailing whitespace.
3412: Refactor common manifest munging in API Collections controller.
3412: Make non-database fields selectable from API server.

This makes it possible to pass method-back field names, like
"data_size" and "files" from Collections, to the select parameter.
3412: Make manifest_text selectable from Collections index API.
Merge branch '3412-full-collections-index'

Closes #3412, #3534.