Adopt license management via Reuse project/tool (#711)

* reuse-managed license/copyright headers

reuse is a tool for compliance with the REUSE recommendations. See
<https://reuse.software/> for more information, and
<https://reuse.readthedocs.io/> for the online documentation.

* Set jsoncpp license
* Add MIT license for Decklink sources
* Explicitly license examples/
  - Add headers to source files
  - Change blanket licensing in .reuse/dep5 to only cover binary media
  - Import CC-BY-3.0 license and assign to sintel_trailer

tests/KeyFrame.cpp

@@ -6,27 +6,9 @@
  * @ref License
  */
 
-/* LICENSE
- *
- * Copyright (c) 2008-2019 OpenShot Studios, LLC
- * <http://www.openshotstudios.com/>. This file is part of
- * OpenShot Library (libopenshot), an open-source project dedicated to
- * delivering high quality video editing and animation solutions to the
- * world. For more information visit <http://www.openshot.org/>.
- *
- * OpenShot Library (libopenshot) is free software: you can redistribute it
- * and/or modify it under the terms of the GNU Lesser General Public License
- * as published by the Free Software Foundation, either version 3 of the
- * License, or (at your option) any later version.
- *
- * OpenShot Library (libopenshot) is distributed in the hope that it will be
- * useful, but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
- * GNU Lesser General Public License for more details.
- *
- * You should have received a copy of the GNU Lesser General Public License
- * along with OpenShot Library. If not, see <http://www.gnu.org/licenses/>.
- */
+// Copyright (c) 2008-2019 OpenShot Studios, LLC
+//
+// SPDX-License-Identifier: LGPL-3.0-or-later
 
 #include <catch2/catch.hpp>