Fix layout of the cards on the guidelines page

See https://hifis-review-app.hzdr.de/review-apps/hifis-hifis-net/fix-guidelines/guidelines

_includes/cards/event_card.html

+{%- comment -%}
+
+This is a card displaying event title and date.
+Parameters:
+event: The event which sould be displayed on the card
+
+{%- endcomment -%}
+<div class="card bg-light">
+    <div class="card-body card-overlay">
+        <div class="card-title">
+            <span class="badge badge-secondary">
+                <i class="fas fa-calendar-day" aria-hidden="true"></i>
+                {{ include.event.date | date: "%d.&thinsp;%b.&thinsp;%y" }}
+            </span>
+            <span class="badge badge-secondary">
+                <i class="fas fa-tag" aria-hidden="true"></i>
+                {{ include.event.type | capitalize }}
+            </span>
+        </div>
+        <div class="card-text">
+            <a href="{{ include.event.url | relative_url }}" class="stretched-link">
+                <h4>{{ include.event.title }}</h4>
+            </a>
+        </div>
+    </div>
+</div>