Add a signal/method to polish the generated files: This phase happens after all files
are written to disk and are ready. It is intended for tasks not directly related to
the project setup: E.g. generation of config files, etc.

Use this to generate our config files.

Change-Id: I9bb5d296bec19f163b70c5ec8d43d5b8e3a52d79
Reviewed-by: Tobias Hunger <tobias.hunger@theqtcompany.com>