fix: added meta robots: noindex, nofollow to changelog, forms and page revisions

This was brought up in #133. Removing the changelog and forms from
search indices makes sense in general. Adding the meta tag to pages with
a specific revision helps to make sure that traffic coming from search
enginges is directed to the most recent version of a page.

Author: redimp

otterwiki/templates/changelog.html

@@ -1,5 +1,9 @@
 {# vim: set et ts=8 sts=4 sw=4 ai: #}
 {% extends "wiki.html" %}
+{%block head %}
+{{ super() }}
+<meta name="robots" content="noindex, nofollow"/>
+{% endblock %}
 {% block content %}
 <div class="w-full mw-full p-0 clearfix">
     <h2 class="float-left">Changelog</h2>

otterwiki/templates/form.html

@@ -1,5 +1,9 @@
 {# vim: set et ts=8 sts=4 sw=4 ai: #}
 {% extends "wiki.html" %}
+{%block head %}
+{{ super() }}
+<meta name="robots" content="noindex, nofollow"/>
+{% endblock %}
 {% block content %}
 <div class="col-sm-12 col-md-12 col-lg-10">
 <div class="card">

otterwiki/templates/page.html

@@ -1,5 +1,11 @@
 {#- vim: set et ts=8 sts=4 sw=4 ai: -#}
 {% extends "wiki.html" %}
+{%block head %}
+{{ super() }}
+{%-if revision %}
+<meta name="robots" content="noindex"/>
+{%-endif%}
+{% endblock %}
 {% block js %}
 {{ super() }}
 <script src="{{ url_for("static", filename="js/polyfill.e6.min.js") | debug_unixtime }}"></script>