fix drag and drop in firefox; rm box-shadow from required inputs

src/css/_layout.scss

@@ -23,6 +23,11 @@ header {
 
 input, button {
   font-family: 'Open Sans';
+  outline: none;
+}
+
+input:required {
+  box-shadow: none;
 }
 
 .btn {

src/js/components/Chessboard.js

@@ -210,6 +210,8 @@ const Column = React.createClass({
   },
   _onDragStart(e) {
     e.dataTransfer.effectAllowed = 'move';
+    // setData is required by firefox
+    e.dataTransfer.setData('text/plain', '');
     this.props.setMoveFrom(this.props.square);
   },
   _onDragOver(e) {