Redesign post cards on frontpage

• Use default font instead of Hermann
• Reduce size by removing the image and some metainformation

Relates to #47 (closed) and !46 (closed)

_includes/cards/post_card.html

+{%- comment -%}
+
+This is a card displaying post title and date.
+Parameters:
+post: The post which sould be displayed on the card
+
+{%- endcomment -%}
+{%- if include.post.title_image == "default" %}
+{%- assign img_url = site.directory.images
+    | append: 'HIFIS_LOGO_news_cards_equal.svg'
+    | strip 
+    | relative_url -%}
+{%- else -%}
+{%- assign img_url = site.directory.large_images
+    | append: "phone/"
+    | append: include.post.title_image
+    | strip 
+    | relative_url -%}
+{%- endif -%}
+<div class="card image-card bg-primary">
+    <img src="{{ img_url }}" class="card-img" alt="Title image for {{ post.title }}">
+    <div class="card-img-overlay">
+        <div class="card-title">
+            <span class="badge badge-secondary">
+                <i class="fas fa-calendar-day" aria-hidden="true"></i>
+                {{ include.post.data | date: "%d.&thinsp;%b.&thinsp;%y" }}
+            </span>
+        </div>
+        <div class="card-text">
+            <a href="{{ include.post.url | relative_url }}" class="stretched-link">
+                <h4>{{ include.post.title }}</h4>
+            </a>
+        </div>
+    </div>
+</div>