Avoid unidecode

[tomdyson]

See wagtail/wagtail#3311:

The problem comes from Unidecode, which is GPL v2 (https://github.com/avian2/unidecode/blob/master/LICENSE). This license is a so-called contaminant license. All derivative works resulting from the integration of the software component are therefore theoretically contaminated and should therefore be distributed with the same license. Wagtail should be GPL v2.

Unfortunately, this license is very contaminating and therefore poses many integration problems - which limits the possibilities of use and integrate your piece of software."

[BertrandBordage]

We will follow what Wagtail does:

• If Wagtail doesn’t require unidecode but uses it when installed, then this project will have the same behaviour.
• If Wagtail decides to avoid transliteration, we will use the unaccent PostgreSQL extension if available. I suggest by the way that we detect if it’s present only when loading the app to avoid extra SQL queries.

[jaap3]

We currently don't require unidecode in setup.py so a small shim could be added to define it conditionally.

[BertrandBordage]

I propose we keep this issue open until we have a better solution.

[jaap3]

Unidecode might also be too aggressive in transliteration, i.e. '北亰' converts to 'Bei Jing'. This might be unexpected behaviour for people trying to search using non latin characters.

[BertrandBordage]

@jaap3, could you explain why it’s a problem that '北亰' converts to 'Bei Jing'? I know nothing about ideograms, so I’d like to know to find a proper solution :)