REEF-43: Get version number from pom (via properties file)

This addresses https://issues.apache.org/jira/browse/REEF-43

The injectable class `Version` now gets the version number from pom (via a properties file).

Yes, [variable replacement](http://maven.apache.org/plugins/maven-resources-plugin/examples/filter.html) is turned on by setting `<filtering>true</filtering>` on the resource. (The name "filtering" is misleading.)