bug 1461350: Add more language middlewares
bug 1461350: Add more language middlewares

Add middlewares for Kuma-specific locale features, provided in to
LocaleURLMiddleware or elsewhere, to keep LocaleMiddleware close to
Django's version.

LangSelectorMiddleware handles locale redirects based on the ?lang query
parameter.

LocaleStandardizerMiddleware redirects to standardize local prefix
cases, legacy locales, and overly specific locales, rather than return
404s.

escattone/kuma,a2sheppy/kuma,Elchi3/kuma,mozilla/kuma,a2sheppy/kuma,SphinxKnight/kuma,SphinxKnight/kuma,escattone/kuma,jwhitlock/kuma,a2sheppy/kuma,mozilla/kuma,a2sheppy/kuma,Elchi3/kuma,jwhitlock/kuma,mozilla/kuma,Elchi3/kuma,SphinxKnight/kuma,mozilla/kuma,Elchi3/kuma,mozilla/kuma,SphinxKnight/kuma,SphinxKnight/kuma,SphinxKnight/kuma,jwhitlock/kuma,Elchi3/kuma,jwhitlock/kuma,a2sheppy/kuma,jwhitlock/kuma,escattone/kuma