show errors if file name is invalid

client/modules/IDE/components/NewFileForm.js

@@ -24,6 +24,7 @@ class NewFileForm extends React.Component {
           {...name}
         />
         <input type="submit" value="Add File" aria-label="add file" />
+        {name.touched && name.error && <span className="form-error">{name.error}</span>}
       </form>
     );
   }

client/styles/components/_modal.scss

@@ -32,6 +32,11 @@
   margin-bottom: #{20 / $base-font-size}rem;
 }
 
+.new-file-form, .new-file-folder {
+  display: flex;
+  flex-wrap: wrap;
+}
+
 .new-file-form__name-label, .new-folder-form__name-label {
   @extend %hidden-element;
 }