Card Details, add plus button in custom fields section

client/components/cards/cardDetails.jade

@@ -257,6 +257,7 @@ template(name="cardDetails")
             else
               input.toggle-switch(type="checkbox" id="toggleCustomFieldsGridButton")
             label.toggle-label(for="toggleCustomFieldsGridButton")
+          a.fa.fa-plus.js-custom-fields.card-details-item.custom-fields(title="{{_ 'custom-fields'}}")
 
       if getVoteQuestion
         hr

client/components/cards/cardDetails.js

@@ -411,6 +411,7 @@ BlazeComponent.extendComponent({
         'click .js-end-date': Popup.open('editCardEndDate'),
         'click .js-show-positive-votes': Popup.open('positiveVoteMembers'),
         'click .js-show-negative-votes': Popup.open('negativeVoteMembers'),
+        'click .js-custom-fields': Popup.open('cardCustomFields'),
         'mouseenter .js-card-details'() {
           if (this.parentComponent() === null) return;
           const parentComponent = this.parentComponent().parentComponent();

client/components/cards/cardDetails.styl

@@ -230,6 +230,9 @@ avatar-radius = 50%
         word-wrap: break-word
         max-width: 28%
         flex-grow: 1
+      &.custom-fields
+        padding-left: 10px
+
 
   .card-details-item-title
     font-size: 16px