Add option to log to file

[oraculix]

First of all: Thank you for sharing your work with the community! It is quite helpful in iterating towards an optimized (and working) ora2pg.conf.

The issue I have when monitoring a running migration in the browser, a glitch in the network connection (or simply an accidental reload) "loses" the event stream.

Particularly for long-running migrations there should be an option to log to a file in the project directory.

Cheers, Uwe