Logging configurable by environment variables

* Configure logging through environment variables.
* Describe how to use it.
* Compile trace logging in by default again. Can still be disabled by a
  compile switch, to get some more performance.
* Disable most of the logging in tests.
1 job for logconfig in 1 minute and 14 seconds
Status Job ID Name Coverage
  Test
passed #3131
test

00:01:14