Fix info addon prop tables (#1607)

Prop Tables were being key'd by their component's object `name` prop; this means that only the first component, of many components of the same type, would show.

Making sure we first check `displayName` for key usage means that components with the same type can all appear in the Prop Tables if their individual `displayName`'s were different.

Case: Higher Order Components

addons/info/src/components/Story.js

@@ -349,7 +349,7 @@ export default class Story extends React.Component {
 
     const { maxPropObjectKeys, maxPropArrayLength, maxPropStringLength } = this.props;
     const propTables = array.map(type =>
-      <div key={type.name}>
+      <div key={type.displayName || type.name}>
         <h2 style={this.state.stylesheet.propTableHead}>
           "{type.displayName || type.name}" Component
         </h2>