Localization of human-readable dates

[eugeneandrienko]

Hello. I found what human-readable dates on the main page of Prosopopee-based gallery are always in English language disregarding to locale settings of my OS. So, I do some changes and now Prosopopee watches to LC_TIME environment variable before format human-readable dates. For example:

• If you use LC_TIME=en_US.utf8 — you will get dates like «23 August 2020» on the your browser with opened gallery;
• If you use LC_TIME=ru_RU.utf8 — you will get «23 Августа 2020»;

For users, who want to have human-readable dates not based on LC_TIME environment variable — I add key «date_locale» for Prosopopee settings.

[Psycojoker]

Manually merged (with rebased etc...) and added you as a contributor, thx a lot :)

I'm not really working on prosopopee myself, I've more or less delegated the project to beudbeud but since he doesn't seems to have time for that right now I'm going to try to take a bit of time to merge what I can myself (but I'm quite busy myself)