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/period_archives.html

@@ -0,0 +1,18 @@
+{% extends "base.html" %}
+
+{% block title %}
+Archives for {{ period | reverse | join(' ') }} {{ super() }}
+{% endblock %}
+
+{% block page_header %}
+Archives for {{ period | reverse | join(' ') }}
+{% endblock %}
+
+{% block content %}
+<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 %}