Fix a bug in Log.error(Object, Throwable)

## Context 
We needed to use `Log.error(Object, Throwable)` but logs were sent at debug level instead of error level.

## Description
- Move of the `Chronometer` class from `codjo-mad-server` to `codjo-util`;
- Fix the bug in `Log.error(Object, Throwable)`;
- Complete the `.gitignore file` to filter log files.