[SPARK-10833] [BUILD] Inline, organize BSD/MIT licenses in LICENSE

In the course of https://issues.apache.org/jira/browse/LEGAL-226 it came to light that the guidance at http://www.apache.org/dev/licensing-howto.html#permissive-deps means that permissively-licensed dependencies has a different interpretation than we (er, I) had been operating under. "pointer ... to the license within the source tree" specifically means a copy of the license within Spark's distribution, whereas at the moment, Spark's LICENSE has a pointer to the project's license in the other project's source tree.

The remedy is simply to inline all such license references (i.e. BSD/MIT licenses) or include their text in "licenses" subdirectory and point to that.

Along the way, we can also treat other BSD/MIT licenses, whose text has been inlined into LICENSE, in the same way.

The LICENSE file can continue to provide a helpful list of BSD/MIT licensed projects and a pointer to their sites. This would be over and above including license text in the distro, which is the essential thing.

Author: Sean Owen <sowen@cloudera.com>

Closes #8919 from srowen/SPARK-10833.