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).

I agree with Brian. The version of REEF is, for better or worse, a long string. And as long as we are in incubation, it has to contain  `-incubating`. And the `-snapshot` indicates that the build at hand isn't a release, but a snapshot. 

The majority use case of this functionality is to drop the version of REEF running into all log files. For that, we should be as specific as we can be.