Change the message shown in the image upload dialog box

This changes the text we display in the image upload dialog box, to
match what is on the mockups (see the linked issue).

closes #1127
pr #1338

static/js/components/ImageUploaderForm.js

@@ -124,7 +124,8 @@ export default class ImageUploaderForm<Form> extends React.Component<
         onDropRejected={() => this.setPhotoError("Please select a valid photo")}
       >
         <div className="desktop-upload-message">
-          Drag a photo here or click to select a photo.
+          Drag an image here<br />or<br />
+          <button className="outlined">Click to select an image</button>
         </div>
         <div className="mobile-upload-message">Click to select a photo.</div>
       </Dropzone>