Fix a structure of pom.xml that Eclipse and IDEA IDEs were complaining about.

An additional <pluginManagement> section was added to the build section of the pom.xml in order to solve “Plugin execution not covered by lifecycle configuration" error generated by Eclipse. IDEA did also stop complaining about jacoco-maven-plugin after this change.
Effectively there are just two lines were added to the pom.xml: <pluginManagement> and </pluginManagement>
For the details on the error, please see http://stackoverflow.com/questions/6352208/how-to-solve-plugin-execution-not-covered-by-lifecycle-configuration-for-sprin