Add code evaluation settings for blink and post evaluate message

[okhick]

The evaluation background decorator had a bug where instead of applying the timeout value, it just flashed. I also shortened the timeout to 600ms, which I think is the SCIDE default. This timeout value could probably be a setting someday.

[okhick]

Reworked it a little. This PR now includes the following:

• I'm not the most familiar with the style of code formatting. I added an extension to format on save (xaver.clang-format). I'm happy to remove it's not helpful to anyone else. This did clean up a bit of things, however.
• Extension settings and implementation for blinkDuration and showMessage

This is accomplished by setting codeEvaluationSettings in SuperColliderContext and then passing the context to evaluateString. This pattern should make it easy to inject more settings if we need to.