add imprint as flatpage

- add flatpages app to gnuviechadmin.settings.base.DJANGO_APPS
- add imprint handling to gnuviechadmin.context_processors.navigation, remove
  unused about page handling
- add URL 'imprint' to gnuviechadmin.urls
- replace link 'about' in template base.html with 'imprint'
- add templates for flatpages
- add german translation for imprint and contact navigation links

gnuviechadmin/templates/base.html

@@ -64,8 +64,8 @@
                 <li><a href="{{ phppgadmin_url }}" title="{% trans "phpPgAdmin - PostgreSQL database administration tool" %}"><i class="icon-postgres"></i> {% trans "phpPgAdmin" %}</a></li>
               </ul>
             </li>
-            <li{% if active_item == 'about' %} class="active"{% endif %}><a href="#about">About</a></li>
-            <li{% if active_item == 'contact' %} class="active"{% endif %}><a href="#contact">Contact</a></li>
+            <li{% if active_item == 'imprint' %} class="active"{% endif %}><a href="{% url 'imprint' %}">{% trans "Imprint" %}</a></li>
+            <li{% if active_item == 'contact' %} class="active"{% endif %}><a href="#contact">{% trans "Contact" %}</a></li>
           </ul>
           <ul class="nav navbar-nav navbar-right">
             {% if user.is_authenticated %}

gnuviechadmin/templates/flatpages/base.html

@@ -0,0 +1 @@
+{% extends "base.html" %}

gnuviechadmin/templates/flatpages/default.html

@@ -0,0 +1,9 @@
+{% extends "flatpages/base.html" %}
+
+{% block title %}{{ block.super }} - {{ flatpage.title }}{% endblock title %}
+
+{% block page_title %}{{ flatpage.title }}{% endblock page_title %}
+
+{% block content %}
+{{ flatpage.content }}
+{% endblock content %}