Bug 568879: [Build] fix warnings, add code checkers

  enforce maven version

Change-Id: I198cf39ff90940ca51585c5df62b1f0d61e1762b
diff --git a/pom.xml b/pom.xml
index 077b8c8..42b8b05 100644
--- a/pom.xml
+++ b/pom.xml
@@ -34,10 +34,7 @@
 			<organizationUrl></organizationUrl>
 		</developer>
 	</developers>
-	<prerequisites>
-		<maven>3.0</maven>
-	</prerequisites>
-
+	
 	<name>Skills (Incubation)</name>
 	<description>Skills adds gamification features to the Eclipse IDE</description>
   
@@ -52,4 +49,29 @@
 	<modules>
 		<module>releng/org.eclipse.skills.releng</module>
 	</modules>
+
+	<build>
+		<plugins>
+			<plugin>
+				<groupId>org.apache.maven.plugins</groupId>
+				<artifactId>maven-enforcer-plugin</artifactId>
+				<version>3.0.0-M3</version>
+				<executions>
+					<execution>
+						<id>enforce-maven</id>
+						<goals>
+							<goal>enforce</goal>
+						</goals>
+						<configuration>
+							<rules>
+								<requireMavenVersion>
+									<version>3.6.0</version>
+								</requireMavenVersion>
+							</rules>
+						</configuration>
+					</execution>
+				</executions>
+			</plugin>
+		</plugins>
+	</build>
 </project>  
diff --git a/releng/org.eclipse.skills.releng/pom.xml b/releng/org.eclipse.skills.releng/pom.xml
index e7590a7..bba8c24 100644
--- a/releng/org.eclipse.skills.releng/pom.xml
+++ b/releng/org.eclipse.skills.releng/pom.xml
@@ -7,12 +7,6 @@
 	<version>0.1.0-SNAPSHOT</version>
 	<packaging>pom</packaging>
 
-	<prerequisites>
-		<!-- Maven 3.1.0 is the earliest version using Eclipse Aether, Maven 3.0.x 
-			uses the incompatible predecessor Sonatype Aether -->
-		<maven>3.1</maven>
-	</prerequisites>
-
 	<properties>
 		<!-- used plugin versions -->
 		<tycho.version>1.5.0</tycho.version>
@@ -44,6 +38,27 @@
 
 	<build>
 		<plugins>
+			<plugin>
+				<groupId>org.apache.maven.plugins</groupId>
+				<artifactId>maven-enforcer-plugin</artifactId>
+				<version>3.0.0-M3</version>
+				<executions>
+					<execution>
+						<id>enforce-maven</id>
+						<goals>
+							<goal>enforce</goal>
+						</goals>
+						<configuration>
+							<rules>
+								<requireMavenVersion>
+									<version>3.6.0</version>
+								</requireMavenVersion>
+							</rules>
+						</configuration>
+					</execution>
+				</executions>
+			</plugin>
+			
 			<!-- enable tycho build extension -->
 			<plugin>
 				<groupId>org.eclipse.tycho</groupId>