Add maven wrapper and enforcer plugin

[mathieucarbou]

To be consistent with other project and avoid dependency problems

      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-enforcer-plugin</artifactId>
        <version>1.4.1</version>
        <executions>
          <execution>
            <id>enforce-java</id>
            <goals>
              <goal>enforce</goal>
            </goals>
            <configuration>
              <rules>
                <dependencyConvergence>
                  <uniqueVersions>false</uniqueVersions>
                </dependencyConvergence>
                <requireJavaVersion>
                  <version>[${java.version},)</version>
                </requireJavaVersion>
                <requireMavenVersion>
                  <version>[${maven.version}]</version>
                </requireMavenVersion>
              </rules>
            </configuration>
          </execution>
        </executions>
      </plugin>

See as an example Terracotta-OSS/terracotta-platform#321