Add Piwik tracking code to sidebar

We can not use layout.html due to
https://github.com/rtfd/readthedocs.org/issues/152Signed-off-by: Michal Čihař <michal@cihar.com>

docs/_templates/layout.html → docs/_templates/piwik.html

-{% extends "layout.html" %}
-
-{% block footer %}
-{{ super() }}
 {% if READTHEDOCS %}
 <!-- Piwik -->
 <script type="text/javascript">
@@ -19,5 +15,4 @@
 <noscript><p><img src="//stats.cihar.com/piwik.php?idsite=17" style="border:0;" alt="" /></p></noscript>
 <!-- End Piwik Code -->
 {% endif %}
-FOOTER
-{% endblock %}
+PIWIK!

docs/conf.py

@@ -146,7 +146,9 @@ html_static_path = ['_static']
 #html_use_smartypants = True
 
 # Custom sidebar templates, maps document names to template names.
-#html_sidebars = {}
+html_sidebars = {
+    '**': 'piwik.html',
+}
 
 # Additional templates that should be rendered to pages, maps page names to
 # template names.