WIP Normalize for diacritics

PR branch for #729

Tasks to do
- [x] unicode normalization client side for page search with unorm and xregexp
- [x] unicode normalization for ES queries, setting up analyzers
- [x] unicode normalization for backend stream
- [x] add tests
- [ ] launch a showcase dokku instance 
`asciifolding` already returns results different from the clientside code (see below) so this change is fine.

original | asciifolding | current JS | icu_folding
--------- | ---------------- | -------------- | -----------------
STARGΛ̊TE SG-1, a = v̇ = r̈, a⃑ ⊥ b⃑ | stargλ̊te sg-1, a = v̇ = r̈, a⃑ ⊥ b⃑ | stargλte sg-1, a = v = r, a ⊥ b | stargλte sg-1, a = v = r, a ⊥ b
Σὲ γνωρίζω ἀπὸ τὴν κόψη | σὲ γνωρίζω ἀπὸ τὴν κόψη | σε γνωριζω απο την κοψηb | σε γνωριζω απο την κοψη
カタカナコンバータ | カタカナコンバータ | カタカナコンバータ |  カタカナコンハタ

If anything, I'd say `icu_folding` is closer to the current frontend behaviour.