Add includes for static-based comments powered by Staticman

- Configure Staticman with sane defaults
- Build comment form to capture new comments and ajax data to Staticman
- Build comments view that iterates over `_data/comments/post-slug/*.yml` files

_includes/comments-providers/staticman.html

@@ -0,0 +1,52 @@
+{% if site.repository and site.staticman.branch %}
+  <!-- Start comment form modal -->
+  <article class="modal">
+    <h2 class="modal__title js-modal-title"></h2>
+    <div class="modal__supporting-text js-modal-text"></div>
+    <div class="modal__actions">
+      <button class="btn btn--danger js-close-modal">Close</button>
+    </div>
+  </article>
+  <!-- End comment form modal -->
+
+  <script>
+    (function ($) {
+    var $comments = $('.js-comments');
+
+    $('.js-form').submit(function () {
+      var form = this;
+
+      $(form).addClass('form--loading');
+
+      $.ajax({
+        type: $(this).attr('method'),
+        url: $(this).attr('action'),
+        data: $(this).serialize(),
+        contentType: 'application/x-www-form-urlencoded',
+        success: function (data) {
+          showModal('{{ site.data.ui-text[site.locale].comment_success_title | default: "Comment submitted" }}', '{{ site.data.ui-text[site.locale].comment_success_msg | default: "Thanks for your comment! It will show on the site once it has been approved." }}');
+          $(form).removeClass('form--loading');
+        },
+        error: function (err) {
+          console.log(err);
+          showModal('{{ site.data.ui-text[site.locale].comment_error_title | default: "Error" }}', '{{ site.data.ui-text[site.locale].comment_error_msg | default: "Sorry, there was an error with your submission. Please make sure all required fields have been completed and try again." }}');
+          $(form).removeClass('form--loading');
+        }
+      });
+
+      return false;
+    });
+
+    $('.js-close-modal').click(function () {
+      $('body').removeClass('show-modal');
+    });
+
+    function showModal(title, message) {
+      $('.js-modal-title').text(title);
+      $('.js-modal-text').html(message);
+
+      $('body').addClass('show-modal');
+    }
+  })(jQuery);
+  </script>
+{% endif %}