[WIP] Introduce text to speech messages

[morckx]

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Seems to work fine. Note that I select the locale for TTS on start up, depending on whether a certain string resource is localized for the current locale und use US locale as fallback otherwise. Switching tts locales dynamically for individual messages used to be too slow, but we can test that again.

TODO: add some settings and check if current ui is android auto.