Quickstarts: Add Maven compiler properties and remove Maven plugin from the the quickstart POM files

1. Make sure the following properties are defined in each quickstart POM file:

<maven.compiler.target>1.6</maven.compiler.target>
<maven.compiler.source>1.6</maven.compiler.source>

2. Remove the Maven plugin from each quickstart POM file:

<!-- Compiler plugin enforces Java 1.6 compatibility and activates annotation processors -->
<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<version>${version.compiler.plugin}</version>
<configuration>
<source>${maven.compiler.source}</source>
<target>${maven.compiler.target}</target>
</configuration>
</plugin>