Use cairo for all drawing operations in i3bar.

fixes #1878

i3bar/src/outputs.c

@@ -151,7 +151,8 @@ static int outputs_start_map_cb(void *params_) {
         new_output->name = NULL;
         new_output->ws = 0,
         memset(&new_output->rect, 0, sizeof(rect));
-        new_output->bar = XCB_NONE;
+        memset(&new_output->bar, 0, sizeof(surface_t));
+        memset(&new_output->buffer, 0, sizeof(surface_t));
 
         new_output->workspaces = smalloc(sizeof(struct ws_head));
         TAILQ_INIT(new_output->workspaces);