open-uri: basic support for proposed intent Implements

Add support for reading URI handlers from a proposed addendum to
the intents-spec in the form:

```ini
[Implements org.freedesktop.UriHandler]
Patterns=*.openstreetmap/node/*;*.openstreetmap/way/*;
```

src/open-uri.c

@@ -523,6 +523,47 @@ uri_handler_free (UriHandler *handler)
 /*
  * Temporary deserialization
  */
+static GPtrArray *
+uri_handler_deserialize_implements (GKeyFile *keyfile)
+{
+  const char *group = "Implements org.freedesktop.UriHandler";
+  g_auto (GStrv) patterns = NULL;
+  GPtrArray *ret = NULL;
+
+  g_assert (keyfile != NULL);
+
+  patterns = g_key_file_get_string_list (keyfile, group, "Patterns", NULL, NULL);
+  if (patterns == NULL)
+    return NULL;
+
+  ret = g_ptr_array_new_with_free_func ((GDestroyNotify)uri_handler_free);
+  for (size_t i = 0; patterns[i] != NULL; i++)
+    {
+      UriHandler *handler = NULL;
+      g_auto (GStrv) pattern_parts = NULL;
+
+      pattern_parts = g_strsplit (patterns[i], "/", 2);
+      if (pattern_parts[0] == NULL)
+        continue;
+
+      handler = g_new0 (UriHandler, 1);
+      handler->hosts = g_new0 (char *, 2);
+      handler->hosts[0] = g_strdup (pattern_parts[0]);
+      if (pattern_parts[1] != NULL)
+        {
+          handler->paths = g_new0 (char *, 2);
+          handler->paths[0] = g_strconcat ("/", pattern_parts[1], NULL);
+        }
+
+      g_ptr_array_add (ret, g_steal_pointer (&handler));
+    }
+
+  if (ret->len == 0)
+    g_clear_pointer (&ret, g_ptr_array_unref);
+
+  return ret;
+}
+
 static GPtrArray *
 uri_handler_deserialize_sections (GKeyFile *keyfile)
 {
@@ -609,7 +650,15 @@ uri_handler_load_keyfiles (void)
       if (!g_key_file_load_from_file (keyfile, filepath, G_KEY_FILE_NONE, NULL))
         continue;
 
-      handlers = uri_handler_deserialize_sections (keyfile);
+      if (g_key_file_has_group (keyfile, "Implements org.freedesktop.UriHandler"))
+        {
+          handlers = uri_handler_deserialize_implements (keyfile);
+        }
+      else
+        {
+          handlers = uri_handler_deserialize_sections (keyfile);
+        }
+
       if (handlers != NULL && handlers->len > 0)
         {
           g_autofree char *basename = NULL;