Add option for a custom text pronunciation dictionary

[paulpv]

it is a well known TTS problem, even with some AI natural language TTS, that some words don't pronounce well.

Examples:

• regex Sounds like "rejects"
• From personal experience, branded app caps words such as "LOCKLY" are almost always pronounced "L" "O" "C" "K" "L" "Y".

A list of examples would never be exhaustive.

Regardless of any list of examples, a user would inevitably eventually want to be able to customize the pronunciation of some words.
Hopefully this can be handled with a fairly simple UI that provides:

1. a list of custom words showing the word and the custom pronunciation
2. a button to add a pair (word -> pronunciation)
3. a button to edit a pair
4. a button to delete a pair
5. a button to test the pronunciation
6. OK/Save/Close as appropriate