First attempt to services section

- base.py: add settings to load GlasfaserServicesPlugin by default
    - glasfaser_cms_page.html: create a placeholder for services
    - cms_plugins.py: add the plugin code
    - models.py: add UngelichTextSectionWithImage model

ungleich_page/models.py

@@ -21,3 +21,12 @@ class UngelichContactUsSection(CMSPlugin):
 class UngelichTextSection(CMSPlugin):
     title = models.CharField(max_length=200)
     description = HTMLField()
+
+
+class UngelichTextSectionWithImage(UngelichTextSection):
+    image = FilerImageField(
+        null=True,
+        blank=True,
+        related_name="utswi_image",
+        on_delete=models.SET_NULL
+    )