fix dir/lookup and col/delete api

1, Fix Layouts first letter capitalized
2, Return http 204 when delete a collection

Signed-off-by: Lei Liu <lei01.liu@horizon.ai>

weed/topology/topology_map.go

@@ -23,7 +23,7 @@ func (t *Topology) ToMap() interface{} {
 			}
 		}
 	}
-	m["layouts"] = layouts
+	m["Layouts"] = layouts
 	return m
 }