Removed hard-coded brand and author information

Signed-off-by: Jim Martens <github@2martens.de>

_data/author.yml

@@ -1,5 +1,7 @@
 name: Jim Martens
-image: /assets/images/jim.jpg
+image: /assets/images/author.jpg
+brand: 2martens
+brand_logo: /assets/images/brand.svg
 image_desc:
 age: 23
 location: Hamburg, Germany

_includes/header.html

@@ -2,8 +2,8 @@
     <nav class="navbar navbar-expand-lg navbar-light fixed-top">
         <div class="container">
             <a class="navbar-brand" href="{{ site.baseurl }}/">
-                <img src="{% link /assets/images/2martensIco.svg %}" width="30" height="30" class="d-inline-block align-top"
-                     alt="2martens Brand Icon">
+                <img src="{{ site.data.author.brand_image }}" width="30" height="30" class="d-inline-block align-top"
+                     alt="{{ site.data.author.brand }} Brand Icon">
                 {{ site.title }}
             </a>