more taxonomy changes + separate header

too eepy to write a proper commit message

layouts/_default/list.html

@@ -1,11 +1,8 @@
 {{ define "main" }}
 <main>
+    {{ partial "header.html" }}
     <article>
         <header>
-            <nav>
-                <a href="/">home</a>
-                <a href="..">go up</a>
-            </nav>
             <h1>{{ .Title }}</h1>
             <h2>{{ .Description }}</h2>
         </header>