Allow logging to a file

Right now, logging goes through a logging server. This might not be appropriate all the time. As a backup, we should allow a plain file instead. The only concern implementing this is the location of such a log file. The natural place would be inside the directory which is created for optimization. Unfortunately, this is problematic, because it takes some time until this directory is created and there are possible errors before.

Inspect the existing logging setup and the code that creates the optimization directory. Determine a usable file location for failures that occur before that directory exists, then define the expected fallback behavior and verify it with the project's available tests.

Written by the indexing model from the issue text.