Toggle logger output with environment variables

[lukechilds]

Just an idea but it would be cool if you could control the output with environment variables.

Something like:

$ TIMBER_LOGGERS="main,render,custom" yarn run dev

and if you wanted to disable custom due to excessive noise you could launch with:

$ TIMBER_LOGGERS="main,render" yarn run dev

That way you could enable/disable noisy loggers without needing code modifications.

Thoughts?