Updated LICENSE and LICENSE headers

This updates the root POM to use the file LICENSE_HEADER.txt for the license headers. It also adds that file, taken from the Apache licensing tutorial. Also, LICENSE.txt is updated accordingly as well.

All other changes stem from running `mvn license:format` and are purely automatic.

This addresses [REEF-26] (https://issues.apache.org/jira/browse/REEF-26)

This closes #9
Addressing the issues raised in the PR

  * Removed a bogus newline
  * Added a test for the new functionality
Merge branch 'master' of https://git-wip-us.apache.org/repos/asf/incubator-reef into reef-34
Added a missing licensing header