Bug fix : error method now logs at ERROR level

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