Use string context for author label

Problem/Motivation

The Author & License and Source, Author & License field widgets use the term "Author" as the label for the field which specifies the creator of an item.

While this is probably the right term to use in English, there might be other languages where the global translation (e.g., "Autor" in German) might have a different meaning in this context, so we would need a different term.
Again in German, people might prefer the term "Urheber" (originator). Due to the label being translated without context, this is impossible to achieve without changing all occurrences of "Author".

Proposed resolution

Use a string context for the label in both widgets.