docs/conf.py: Configure the 'alabaster' theme

Add the 'navigation' bar to the sidebar, which for some
reason is not enabled by default. Remove 'relations', which
is effectively disabled anyway and isn't useful for us.

This requires that we mandate having at least Sphinx 1.3,
where the theme was added.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Acked-by: Aleksandar Markovic <amarkovic@wavecomp.com>
Message-id: 20190305172139.32662-6-peter.maydell@linaro.org
Message-id: 20190228145624.24885-6-peter.maydell@linaro.org

docs/conf.py

@@ -25,7 +25,8 @@
 
 # If your documentation needs a minimal Sphinx version, state it here.
 #
-# needs_sphinx = '1.0'
+# 1.3 is where the 'alabaster' theme was shipped with Sphinx.
+needs_sphinx = '1.3'
 
 # Add any Sphinx extension module names here, as strings. They can be
 # extensions coming with Sphinx (named 'sphinx.ext.*') or your custom
@@ -106,7 +107,8 @@ html_theme = 'alabaster'
 # refs: http://alabaster.readthedocs.io/en/latest/installation.html#sidebars
 html_sidebars = {
     '**': [
-        'relations.html',  # needs 'show_related': True theme option to display
+        'about.html',
+        'navigation.html',
         'searchbox.html',
     ]
 }