update packaging to use dh_sphinxdoc and dh_python2

requires search-html.patch to fix file so dh_sphinxdoc recognises it

debian/patches/search-html.patch

@@ -0,0 +1,21 @@
+Description: change to ajax load of searchindex
+ required so dh_sphinx recognises it as a search.html
+--- a/doc/source/themes/scikit-image/search.html
++++ b/doc/source/themes/scikit-image/search.html
+@@ -10,7 +10,15 @@
+ {% extends "layout.html" %}
+ {% set title = _('Search') %}
+ {% set script_files = script_files + ['_static/searchtools.js'] %}
+-{% set script_files = script_files + ['searchindex.js'] %}
++{% block extrahead %}
++  <script type="text/javascript">
++    jQuery(function() { Search.loadIndex("{{ pathto('searchindex.js', 1) }}"); });
++  </script>
++  {# this is used when loading the search index using $.ajax fails,
++     such as on Chrome for documents on localhost #}
++  <script type="text/javascript" id="searchindexloader"></script>
++  {{ super() }}
++{% endblock %}
+ {% block body %}
+   <h1 id="search-documentation">{{ _('Search') }}</h1>
+   <div id="fallback" class="admonition warning">

debian/patches/series

@@ -1,2 +1,3 @@
 changeset_0eea2a48fe2dca7bbb3681fcd5b511579cad6347.diff
 up_correct_version
+search-html.patch