Include org.apache.sling.testing.hamcrest in global parents, for easier unit testing

It would be nice to include
```
<dependency>
<groupId>org.apache.sling</groupId>
<artifactId>org.apache.sling.testing.hamcrest</artifactId>
<version></version>
<scope>test</scope>
</dependency>
```
in the global parent, to make unit testing easier with the Sling Hamcrest Matchers.