Add commons-logging dependency as provided to root pom.xml to ensure the dependency does not get included in the runtime environment

Also see http://www.slf4j.org/faq.html#excludingJCL

thx for the idea Mickaël Tricot

<dependency>
<groupId>commons-logging</groupId>
<artifactId>commons-logging</artifactId>
<version>1.1.1</version>
<scope>provided</scope>
</dependency>