ICU support (new)

[tdrz]

Support for multi-language through libicu.

We need to:

1. Build a minimal en_US data package that we deliver by default (Postgres doesn't start without one when building with icu).
2. (Optional) build separately all the other locales/languages and have a separate package for them.
3. Allow users to preload language data before startup

This is work in progress. Help wanted!