relicense: update COPYRIGHT, LICENSE-*, README, CONTRIBUTING, and NOTICE

This updates Spack's top-level metadata files to reflect the new
Apache-2.0 and MIT licenses.

CONTRIBUTING.md

@@ -1,5 +1,8 @@
 # Contributing to Spack
 
-Before contributing to Spack you should read the
+All contributions to Spack must be made under both the Apache License,
+Version 2.0 (Apache-2.0) and the MIT license (MIT).
+
+Before contributing to Spack, you should read the
 [Contribution Guide](https://spack.readthedocs.io/en/latest/contribution_guide.html),
 which is maintained as part of Spack's documentation.

COPYRIGHT

@@ -0,0 +1,85 @@
+Intellectual Property Notice
+------------------------------
+
+Spack is licensed under the Apache License, Version 2.0 (LICENSE-APACHE
+or http://www.apache.org/licenses/LICENSE-2.0) or the MIT license,
+(LICENSE-MIT or http://opensource.org/licenses/MIT), at your option.
+
+Copyrights and patents in the Spack project are retained by contributors.
+No copyright assignment is required to contribute to Spack.
+
+Spack was originally distributed under the LGPL-2.1 license. Consent from
+contributors to relicense to Apache-2.0/MIT is documented at
+https://github.com/spack/spack/issues/9137.
+
+
+SPDX usage
+------------
+
+Individual files contain SPDX tags instead of the full license text.
+This enables machine processing of license information based on the SPDX
+License Identifiers that are available here: https://spdx.org/licenses/
+
+Files that are dual-licensed as Apache-2.0 OR MIT contain the following
+text in the license header:
+
+    SPDX-License-Identifier: (Apache-2.0 OR MIT)
+
+
+External Packages
+-------------------
+Spack bundles its external dependencies in lib/spack/external.  These
+packages are covered by various permissive licenses.  A summary listing
+follows.  See the license included with each package for full details.
+
+PackageName: argparse
+PackageHomePage: https://pypi.python.org/pypi/argparse
+PackageLicenseDeclared: Python-2.0
+
+PackageName: ctest_log_parser
+PackageHomePage: https://github.com/Kitware/CMake
+PackageLicenseDeclared: BSD-3-Clause
+
+PackageName: distro
+PackageHomePage: https://pypi.python.org/pypi/distro
+PackageLicenseDeclared: Apache-2.0
+
+PackageName: functools
+PackageHomePage: https://github.com/python/cpython/blob/2.7/Lib/functools.py
+PackageLicenseDeclared: Python-2.0
+
+PackageName: jinja2
+PackageHomePage: https://pypi.python.org/pypi/Jinja2
+PackageLicenseDeclared: BSD-3-Clause
+
+PackageName: jsonschema
+PackageHomePage: https://pypi.python.org/pypi/jsonschema
+PackageLicenseDeclared: MIT
+
+PackageName: markupsafe
+PackageHomePage: https://pypi.python.org/pypi/MarkupSafe
+PackageLicenseDeclared: BSD-3-Clause
+
+PackageName: orderddict
+Homepage: https://pypi.org/project/ordereddict/
+PackageLicenseDeclared: MIT
+
+PackageName: py
+PackageHomePage: https://pypi.python.org/pypi/py
+PackageLicenseDeclared: MIT
+
+PackageName: pyqver
+PackageHomePage: https://github.com/ghewgill/pyqver
+PackageLicenseDeclared: BSD-3-Clause
+
+PackageName: pytest
+PackageHomePage: https://pypi.python.org/pypi/pytest
+PackageLicenseDeclared: MIT
+
+PackageName: ruamel.yaml
+PackageHomePage: https://yaml.readthedocs.io/
+PackageLicenseDeclared: MIT
+
+PackageName: six
+PackageHomePage: https://pypi.python.org/pypi/six
+PackageLicenseDeclared: MIT