Add field for name etymologies

[1ec5]

There should be Namesake or Name Origin field corresponding to the name:etymology and name:etymology:wikidata keys. These could be separate optional fields, along the lines of #218. We should simultaneously add a special case to iD that avoids treating the etymology subkey as a language code.

Beyond that basic implementation, there may be a desire in some multilingual places to specify a different etymology for different languages, for example name:en:etymology versus name:fr:etymology. But for that extra level of detail, I think we’d first need to resolve a slight disagreement between pronunciation mappers and etymology mappers and introduce something to the schema-builder to differentiate between the parts of a key before and after the language code. Currently, iD assumes a localized field should always append the language code to the end of the key.

/ref #168