[REEF-38] Updates according to Apache RAT output

This updates the code base such that a `mvn apache-rat` passes. To achieve this,
the following files have been updated with license headers:

  * Tang protocol buffers schema files.
  * Tang POM files

The following files and folders have been marked as exclusions from Apache RAT:

  * README.* (this also removes the now unneeded license headers from them)
  * The .bin files in Tang's tests. Those are generated from the C# code base
    at Microsoft and are given to the ASF as a contribution.  They won't be
    needed anymore once we have moved the .NET code base to the ASF as well.
  * REEF_LOCAL_RUNTIME and its subfolders. This directory is sometimes created
    during the tests. It is not actually part of a release, but excluding it and
    the potentially thousands of files inside speeds up Apache RAT quite a bit.
  * Visual Studio project files. These are frequently overwritten, making a
    license header requirement quite cumbersome to support.