[REEF-47]: Log the REEF Version in all processes.

The following changes are made to that end:

  * The new method `REEFVersion.logVersion()` is added which performs the
    actual logging.
  * On the client, this method is called in the constructor of
    `REEFImplementation`.
  * On the Driver and Evaluator, the method is called in the constructor of
    `LaunchClass`

Also, this removes the method `REEF.getVersion()` and its implementation in
`REEFImplementation` as that method wasn't used.

Related JIRAs:
  [REEF-47](https://issues.apache.org/jira/browse/REEF-47)
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