adding support for min/max-width/height

Summary: Adding controls for min/max height/width to the playground

Reviewed By: emilsjolander

Differential Revision: D7988400

fbshipit-source-id: bae487e2504906788552d6c1a29ed74c39cb5ac0

website/src/components/Playground/EditValue.js

@@ -33,7 +33,7 @@ export default (props: Props<*>) => {
         type="text"
         {...props}
         onChange={e => props.onChange(props.property, e.target.value)}
-        placeholder="undefined"
+        placeholder={props.placeholder || 'undefined'}
         onFocus={e => e.target.select()}
         value={Number.isNaN(props.value) ? '' : props.value}
       />