Added maven-profiles to enable switching between yarn and non-yarn hadoop

Here is the proposal to add maven profiles to easily switch between hadoop versions (as discussed last friday). Some comments
* There are two maven profiles: hadoop_yarn (default) and hadoop_v1.
* Maven profiles can be activated with the -P option
* The default profile will be deactivated as soon as another profile becomes active
* I also introduced a new hadoop.version property, that can be changed using the -D option

How to build for yarn using a specific version (e.g. 2.1.0-beta)
```mvn -Dhadoop.version=<version> <goal>```

How to build for any hadoop v1 version (will use hadoop-core):
```mvn -Phadoop_v1 -Dhadoop.version=<version>  <goal>```

The solution was inspired by mahout and giraph https://github.com/apache/giraph.