Add Plugin Management Definition for Clirr

[Kortanul]

Right now, wrensec-parent defines a property for the version of Clirr in use, but doesn't actually use this property itself. Clirr needs to be added to <pluginManagement>, like so:

            <plugins>
                <plugin>
                    <groupId>org.codehaus.mojo</groupId>
                    <artifactId>clirr-maven-plugin</artifactId>
                    <version>${clirrPluginVersion}</version>
                </plugin>
            </plugins>

As of WrenSecurity/wrensec-commons#12, Commons BOM will be compensating for this oversight until it can be addressed in the next Parent release.