implement js and meta-tag redirects

[its-miroma]

this is certainly very buggy still. it also is probably pretty bad for SEO.

JS-based redirect seems to work fine, but meta-tag (which is the one that's acceptable for SEO) is not working at all. the main problem is that I cannot obtain the original path that caused a 404, which means I cannot set up a redirect like this.

I implemented the following redirects for now:

• remove all file extensions (should be already getting done by default)
• remove index as it's implied (again, done by default)
• redirect all URLs to lowercase
• redirect hyphened locales to underscores (it-it -> it_it)
• redirect item-groups to creative-tabs as an example

TODO:

• fix meta-tag implementation
• redirect "it" to "it_it"
  • must be careful with el_gr, ja_jp, ko_kr, ms_my, pt_br, uk_ua, vi_vn, zh_cn / zh_tw
• change references to "Item Groups" to "Creative Tabs"

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