Add full language support

[jwr1]

• Posts and comments now have the associated language attached under Lemmy and PieFed (already existed for Mbin). Unfortunately, this required passing around a list of language codes with language IDs, but I'm not really sure there's a better way to do it.
• Creating a post will correctly set the given language for Lemmy and PieFed (already existed for Mbin).
• Posts and comments now display a little badge with the associated language code, and a tooltip for the full name.
• Add language selection on comment creation.
• Change the defaultPostLang setting to defaultCreateLang (to accommodate being used with both posts and comments).
• Language badge will only display if it's different from defaultCreateLanguage.

[olorin99]

I also added a sort to the language selection menu, otherwise looks good.