Simplify jinja2 base templates, update theme options

- New realfavicongenerator.net packages (https://realfavicongenerator.net/blog/new-favicon-package-less-is-more/)
- Support all possible Pelican feed links
- Add recommended HEAD elements (https://github.com/joshbuchea/HEAD)
- Use minified css assets
- Link to boostrap, clean-blog and font-awesome stylesheets
- Add theme options, better options names

Template consistency, update structure on base.html

Fix missing article summary on index.html

Show the article.summary for teasers

alchemy/templates/archives.html

@@ -1,15 +1,18 @@
 {% extends "base.html" %}
 
 {% block title %}
-  {{ SITENAME }} — Archives
+Archives {{ super() }}
+{% endblock %}
+
+{% block page_header %}
+Archives
 {% endblock %}
 
 {% block content %}
-  <h1>Archives</h1>
-  <dl class="list dl-horizontal">
-    {% for article in dates %}
-      <dt>{{ article.locale_date }}</dt>
-      <dd><a href="{{ SITEURL }}/{{ article.url }}">{{ article.title }}</a></dd>
-    {% endfor %}
-  </dl>
+<dl class="dl-horizontal">
+  {% for article in dates %}
+  <dt>{{ article.locale_date }}</dt>
+  <dd><a href="{{ SITEURL }}/{{ article.url }}">{{ article.title }}</a></dd>
+  {% endfor %}
+</dl>
 {% endblock %}