Added license information to d3 JS file and to the word cloud layout.

common/lib/xmodule/xmodule/js/src/word_cloud/d3.layout.cloud.js

-// Word cloud layout by Jason Davies, http://www.jasondavies.com/word-cloud/
-// Algorithm due to Jonathan Feinberg, http://static.mrfeinberg.com/bv_ch03.pdf
+/*
+ * Word cloud layout by Jason Davies
+ * https://github.com/jasondavies/d3-cloud
+ * 
+ *
+ * Copyright (c) 2012, Jason Davies.
+ * All rights reserved.
+ * 
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ * 
+ *   * Redistributions of source code must retain the above copyright notice, this
+ *     list of conditions and the following disclaimer.
+ * 
+ *   * 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.
+ * 
+ *   * The name Jason Davies may not 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 JASON DAVIES 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.
+ */
 (function(exports) {
   function cloud() {
     var size = [256, 256],