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 
As I suggested previously, you can just use `['icu_folding']` here. It already does normalisation. See

https://github.com/elasticsearch/elasticsearch-analysis-icu/blob/121513dd59a09916876e53057a90787352f02e70/src/main/java/org/elasticsearch/index/analysis/IcuFoldingTokenFilterFactory.java#L69

which is a call to this class in Lucene:

https://github.com/apache/lucene-solr/blob/1943bed963a2dc2bc2b0f7bc62034e37b3e08af2/lucene/analysis/icu/src/java/org/apache/lucene/analysis/icu/ICUFoldingFilter.java#L64-L66

which can be compared with the call that `icu_normalizer` makes:

https://github.com/elasticsearch/elasticsearch-analysis-icu/blob/121513dd59a09916876e53057a90787352f02e70/src/main/java/org/elasticsearch/index/analysis/IcuNormalizerTokenFilterFactory.java#L50

Moreover, I can't find any input for which `icu_normalizer,icu_folding` emits a different output to plain `icu_folding`.