support remaining IPA modifiers in text frontend

[Flux9665]

self-reminder: there are still a lot of unsupported IPA characters, some of which might need the introduction of a new categorical feature in the featurevector (e.g. ejectives). The step towards massviely massively multilingual TTS should take care of those with the new phonemization setups before data caches are extracted.

To check for comleteness this could be helpful: https://www.phonetik.uni-muenchen.de/studium/skripten/Transkription/IPA/IPA.html