Implement text normalization

[galv]

We are lacking text normalization at the moment, which qualifies in my book as a serious flaw.

I recommend Sparrowhawk as a first step: https://github.com/google/sparrowhawk Ideally we would wrap its build system in bazel. But we could also add it to the Dockerfile as well.

[galv]

https://github.com/rhasspy/gruut this may be a good alternative. Multiple languages no C++ dependency to install.