fix deprecated theme config options

- multiple favicons was moved into external sphinx_favicon extension
- footer_items was split into _start, _center, and _end. _start is by
  default what we had configured:
  'copyright', 'sphinx_version'

Change-Id: Ibb238c04deedf198de680f8483288eab63c85b64

requirements.txt

@@ -1,2 +1,3 @@
 pydata-sphinx-theme
 sphinx_design
+sphinx_favicon

source/conf.py

@@ -43,6 +43,7 @@
     'sphinx.ext.todo',
     'sphinx.ext.extlinks',
     'sphinx_design',
+    'sphinx_favicon',
 ]
 
 todo_include_todos = True
@@ -83,26 +84,7 @@
         'image_light': 'logo.svg',
         'image_dark': 'logo.svg',
     },
-    'footer_items': ['copyright'],
     'secondary_sidebar_items': ['page-toc', 'sourcelink'],
-    'favicons': [
-        {
-            'rel': 'icon',
-            'sizes': '16x16',
-            'href': 'favicon16.png',
-        },
-        {
-            'rel': 'icon',
-            'sizes': '32x32',
-            'href': 'favicon32.png',
-        },
-        {
-            'rel': 'apple-touch-icon',
-            'sizes': '180x180',
-            'href': 'favicon.png',
-            'color': '#000000',
-        },
-    ],
     #"announcement": "<em>Important</em> announcement!",
     'header_links_before_dropdown': 4,
     # links with icons to the right of the search icon:
@@ -117,6 +99,26 @@
 html_static_path = ['_static']
 
 
+favicons = [
+    {
+        'rel': 'icon',
+        'sizes': '16x16',
+        'href': 'favicon16.png',
+    },
+    {
+        'rel': 'icon',
+        'sizes': '32x32',
+        'href': 'favicon32.png',
+    },
+    {
+        'rel': 'apple-touch-icon',
+        'sizes': '180x180',
+        'href': 'favicon.png',
+        'color': '#000000',
+    },
+]
+
+
 class SECoPLexer(RegexLexer):
     name = 'secop'
     flags = re.MULTILINE