Don’t set custom emojis `imageUrl` required

+ add missing prop types since #251

src/utils/shared-props.js

@@ -56,7 +56,13 @@ const PickerPropTypes = {
       short_names: PropTypes.arrayOf(PropTypes.string).isRequired,
       emoticons: PropTypes.arrayOf(PropTypes.string),
       keywords: PropTypes.arrayOf(PropTypes.string),
-      imageUrl: PropTypes.string.isRequired,
+      imageUrl: PropTypes.string,
+      spriteUrl: PropTypes.string,
+      sheet_x: PropTypes.number,
+      sheet_y: PropTypes.number,
+      size: PropTypes.number,
+      sheetColumns: PropTypes.number,
+      sheetRows: PropTypes.number,
     }),
   ),
   skinEmoji: PropTypes.string,