💄 Improve button consistency in campaign list

- Change follow button to match FOI request style
- Clarify follow button text
- Change pending request button from warning (yellow) to secondary (gray)
  for consistent visual language

closes fragdenstaat/issues#286

Author: n0ctua

frontend/i18n/campaign-follow.json

@@ -2,11 +2,11 @@
   "en": {
     "unfollow": "Unfollow",
     "followed": "Followed",
-    "follow_q": "Follow?"
+    "follow_q": "Follow request?"
   },
   "de": {
     "unfollow": "Entfolgen",
     "followed": "Gefolgt",
-    "follow_q": "Folgen?"
+    "follow_q": "Anfrage folgen?"
   }
 }

frontend/javascript/components/campaign-follow.vue

@@ -16,14 +16,14 @@
     </button>
     <button
       v-else
-      class="input-large btn hover-btn-success btn-sm"
+      class="input-large btn btn-outline-primary btn-sm"
       @click.stop="doFollow">
       <span class="on-hover">
-        <i class="fa fa-star" aria-hidden="true"></i>
+        <i class="fa fa-bell" aria-hidden="true"></i>
         {{ i18n.follow_q }}
       </span>
       <span class="on-display">
-        <i class="fa fa-star-o" aria-hidden="true"></i>
+        <i class="fa fa-bell-o" aria-hidden="true"></i>
         {{ i18n.follow_q }}
       </span>
     </button>

frontend/javascript/components/campaign-list-item.vue

@@ -107,7 +107,7 @@ export default {
     },
     btnClass() {
       if (this.object.resolution === 'pending') {
-        return 'btn-outline-warning'
+        return 'btn-outline-secondary'
       } else if (this.object.resolution === 'successful') {
         return 'btn-outline-success'
       } else if (this.object.resolution === 'refused') {