Clarify license files.

Based on discussion at jupyter/governance#37 and discussion from the links on that issue, I made the following changes:

1. Delete the COPYING.md, as it was redundant
2. Changed the LICENSE copyright dates to just have the starting year

I also added LICENSE to the widgetsnbextension package (thanks to @jakirkham for noticing this in jupyter-widgets#2048).

This supersedes jupyter-widgets#1706, which was reverted in master while the discussion was still happening.

LICENSE

@@ -1,4 +1,4 @@
-Copyright (c) 2015-2016, Project Jupyter Contributors
+Copyright (c) 2015 Project Jupyter Contributors
 All rights reserved.
 
 Redistribution and use in source and binary forms, with or without

MANIFEST.in

@@ -1,4 +1,4 @@
-include COPYING.md
+include LICENSE
 include CONTRIBUTING.md
 include README.md
 include package.json

widgetsnbextension/LICENSE

@@ -0,0 +1,27 @@
+Copyright (c) 2015 Project Jupyter Contributors
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+1. Redistributions of source code must retain the above copyright notice, this
+   list of conditions and the following disclaimer.
+
+2. Redistributions in binary form must reproduce the above copyright notice,
+   this list of conditions and the following disclaimer in the documentation
+   and/or other materials provided with the distribution.
+
+3. Neither the name of the copyright holder nor the names of its
+   contributors may be used to endorse or promote products derived from
+   this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

widgetsnbextension/MANIFEST.in

@@ -1,3 +1,4 @@
+include LICENSE
 graft widgetsnbextension/static
 graft src
 include package.json