Reuse spinner on pulse page instead of always overwriting it

The spinner is now always in the same position. It was previously
centered during the initial page load, then on the left whenever
changing the selected period in the dropdown. This was caused by the
HTML and CSS classes which differed.

src/api/app/views/webui2/webui/projects/pulse/show.html.haml

@@ -25,10 +25,11 @@
             = link_to(project_pulse_path(@project, range: 'month'), remote: true, type: :json, class: 'dropdown-item') do
               One Month
     .row
-      .col#pulse
+      .col.spinner
         .row
           .col.text-center
             %i.fas.fa-spinner.fa-spin.fa-3x
+      .col.d-none#pulse
 
 :javascript
   $.ajax({
@@ -38,7 +39,7 @@
   });
 
   $(".dropdown-item").click(function() {
-    $("#pulse").html('<div class="fa-3x"><i class="fas fa-spinner fa-spin"></i></div>')
+    $('#pulse, .col.spinner').toggleClass('d-none');
     // FIXME: No idea why this is needed, maybe remote links are not covered by bootstrap?
     $('#period-dropdown').dropdown('toggle')
   });

src/api/app/views/webui2/webui/projects/pulse/show.js.erb

@@ -1,14 +1,15 @@
 $('#range-header').html("<%= escape_javascript(pulse_period(@range)) %>");
 $('#range-text').html("<%= @range.titleize %>");
+$('#pulse, .col.spinner').toggleClass('d-none');
 $('#pulse').html("<%= escape_javascript render partial: 'pulse_list', locals: { requests_by_percentage: @requests_by_percentage,
-                                                                               requests_by_state: @requests_by_state,
-                                                                               project: @project,
-                                                                               commits: @commits,
-                                                                               new_packages: @new_packages,
-                                                                               deleted_packages: @deleted_packages,
-                                                                               updates: @updates,
-                                                                               project_changes: @project_changes,
-                                                                               builds: @builds,
-                                                                               branches: @branches,
-                                                                               comments: @comments,
-                                                                               requests: @requests } %>");
+                                                                                requests_by_state: @requests_by_state,
+                                                                                project: @project,
+                                                                                commits: @commits,
+                                                                                new_packages: @new_packages,
+                                                                                deleted_packages: @deleted_packages,
+                                                                                updates: @updates,
+                                                                                project_changes: @project_changes,
+                                                                                builds: @builds,
+                                                                                branches: @branches,
+                                                                                comments: @comments,
+                                                                                requests: @requests } %>");