Pass a custom logger to use instead of wsgi.errors

As an API developer, I can consolidate all app messages in a single log file so that I don't loose the context of the messages.

It would be cool if wsgi.errors could still (optionally) be written to in tandem.

No file or test is named in the issue. Start by locating where wsgi.errors is used and how application logging is configured. Done means a custom logger can receive app messages, with optional simultaneous writes to wsgi.errors, backed by tests for both modes.

Written by the indexing model from the issue text.