Write logs in log directory 

`crash.log` and `openmw.log` file are created in the working directory, requiring users that had installed the game to run it with augmented privileges to be able to create the file.

This move the initialisation of the configuration manager, which could throw if it cannot create the user data and user config directories. This error can't ends up in crash.log any more.

**Edit:** `openmw.log` now contains a copy of all the text output (stdout and stderr), and is always produced, on all platforms.