title: Rails: custom wrapper for submit button in simple_form?
body: <p>I am using simple_form gem with bootstrap 3.
  I want to have a wrapper for submit button</p>
  
  <p>Now it shows HTML as</p>
  
  <pre><code>&lt;form id="new_order" ...&gt;
      ...
  
     &lt;input class="btn btn-primary" type="submit" value="Save" name="commit"&gt;
  &lt;/form&gt;
  </code></pre>
  
  <p>I want to write a wrapper so the HTML would be:</p>
  
  <pre><code>&lt;form id="new_order" ...&gt;
    ...
  
    &lt;div class="form-group"&gt;
       &lt;div class="col-sm-offset-2 col-sm-10"&gt;
          &lt;input class="btn btn-primary" type="submit" value="Save" name="commit"&gt;
       &lt;/div&gt;
   &lt;/div&gt;
  </code></pre>
  
  <p> </p>
  
  <p>I got this so far:</p>
  
  <p>app/initializers/simple_form_bootstrap.rb:</p>
  
  <pre><code>options[:wrapper] = :horizontal_form
  options[:wrapper_mappings] = {
    check_boxes: :horizontal_radio_and_checkboxes,
    radio_buttons: :horizontal_radio_and_checkboxes,
    file: :horizontal_file_input,
    boolean: :horizontal_boolean,
  
   # what to write here??
   # submit: :horizontal_submit_button
  
  }
  </code></pre>
  
  <p>and this is my wrapper:</p>
  
  <pre><code>  config.wrappers :horizontal_submit_button, tag: 'div', class: 'form-group', error_class: 'has-error' do |b|
       b.use :html5
       b.use :placeholder
  
       b.wrapper tag: 'div', class: 'col-sm-offset-2 col-sm-10' do |ba|
         ba.use :input
         # some coe goes here, maybe
       end
    end
  </code></pre>
  
  <p>Which input type to use in wrapper_mappings for submit button? How to write that wrapper?</p>