Allow only admins to add watermarks

Hello and many thanks for the plugin!
On my site I have several authors who publish posts. Author must not have capability to add watermarks to images in my case.
I think it would be great to add option to the plugin which allows to select minimal role level which opens access to plugins features.

Right now, I hardcoded this feature for admins only in these functions (EasyWatermarkPlugin.php):

public function add_media_page() {
    if ($this->isGDEnabled() && current_user_can('administrator'))
      add_media_page('Easy Watermark', 'Easy Watermark', 'upload_files', 'easy-watermark', array($this, 'easy_watermark'));
  }
public function add_media_row_action($actions, $post, $detached) {
    if ($this->isGDEnabled() && in_array($post->post_mime_type, $this->allowedMime) && current_user_can('administrator')) {
      // Add link if it's supported image type
      $actions['add_watermark'] = '<a href="' . wp_nonce_url(admin_url('upload.php?page=easy-watermark&attachment_id=' . $post->ID . '&r=library')) . '">' . __('Add watermark', 'easy-watermark') . '</a>';
    }
    return $actions;
  }

http://wordpress.org/extend/plugins/easy-watermark/