Settings dialog, TTS voices page: presentation of gender/age info

[marisademeglio]

• The gender/age options could maybe be presented better also. Instead of "Female-adult" etc., maybe something like "Female adult" (or just "Female" or "Woman"), "Female elderly" (or "Old woman"), "Female child" (or "Girl"), "Neutral" (or "Gender neutral"), ...

  In fact "Unknown" would be more accurate than "Neutral". Voices marked "neutral" (or "*", same thing) match any requested gender, so it's effectively like a wildcard. But in practice this category is used primarily for voices for which we can't automatically determined the gender, notably the macOS voices. We should probably make two separate categories.

  (Actually it might be useful to be able to select the gender for which the macOS voice is to be used when it is selected as a preferred voice.)

  Perhaps another possibility would be to have two options, one for gender and one for age, although that might become a bit much.

Originally posted by @bertfrees in #170 (comment)