Re-introduce section IDs

We may have had these before, and they may have been removed because
of concerns that IDs must be unique that non-unique IDs would be
caught by Django-Tidy. Or maybe not, I can't remember.

example/templates/contact.html

@@ -1,5 +1,6 @@
 {% load i18n cms %}
-<section class="contact">
+
+<section class="contact" id="{{section.title|slugify}}">
     <div class="wrapper">
         <div class="title">
             <h1>{{section.title}}</h1>

example/templates/images.html

@@ -1,6 +1,6 @@
 {% load thumbnail i18n cms %}
 
-<section class="images">
+<section class="images" id="{{section.title|slugify}}">
     <div class="images">
         {% for image in section.images.all %}
             <div class="image">

example/templates/text.html

@@ -1,6 +1,6 @@
 {% load i18n cms %}
 
-<section class="text">
+<section class="text" id="{{section.title|slugify}}">
     <div class="wrapper">
         <div class="title">
             <h1>

example/templates/video.html

@@ -1,6 +1,6 @@
 {% load embed_video_tags i18n cms %}
 
-<section class="video">
+<section class="video" id="{{section.title|slugify}}">
     {% if section.video %}
         <div class="video">
             <div class="iframe">