Add "Edit on gitlab" link

Add the link, example can be found at http://hub.pages.pasteur.fr/12765-viralhostrangedb/ and https://gitlab.pasteur.fr/hub/12765-viralhostrangedb/blob/master/doc/conf.py#L72-79

doc/source/conf.py

@@ -181,3 +181,14 @@ napoleon_use_rtype = False  # More legible
 autosummary_generate = True
 
 exclude_patterns = ['_build']
+
+# Edit on gitlab link
+html_context = {
+    "display_gitlab": True, # Integrate Gitlab
+    "gitlab_user": "statistical-genetics", # Username
+    "gitlab_host": "gitlab.pasteur.fr",
+    "gitlab_repo": "jass", # Repo name
+    "gitlab_version": "master", # Version
+    "conf_py_path": "/doc/source/", # Path in the checkout to the docs root
+}
+