Extend `LexicalEntryBuilder` with functions for setting/handling `dcterms` properties

[dsifriend]

While setting Dublin Common Terms properties (creator/author, license, etc.) at a Lexicon level is quite logical and already possible with the LexiconBuilder interface, being able to set those on an entry-by-entry basis would facilitate the creation and handling of multi-source datasets.

These terms are already part of the LexicalEntry interface, so it should only be a matter of implementing the LexicalEntryBuilder methods.