Plugin settings should have a default selection for author/translator roles

[kaitlinnewson]

In 3.4, the plugin settings allow users to select roles for authors and translators. By default, nothing is selected when the plugin is enabled - this results in author information missing from citations when displayed. We should have default selections (e.g. Author = default author role, Translator = default translator role) so that the citations render more correctly when the plugin is enabled.

Possible related forum post: https://forum.pkp.sfu.ca/t/clarification-for-apa-format-for-new-version-of-ojs-3-4-0-6/90166/