Add say correct words feature.

Patch by Debjit Mondal
Add a new option to speak correct words.
New option is enabled by default.
If enabled correctly typed words are spoken by playing the associated sound file.
Reveal word also plays the sound file associated with a word.
Also some whitespace fixes in the changed files.
TODO: Add text to speech for words that don't have sound files associated with them.
REVIEW: 116771