Refactor ISUPPORT handling

Add a helper class to parse ISUPPORT tokens. Instead of having
manual ISUPPORT handling all over the place, use pre-processed
values.

components/buffer-list.js

@@ -44,7 +44,7 @@ export default function BufferList(props) {
 		let server = props.servers.get(buf.server);
 
 		let bouncerNetwork = null;
-		let bouncerNetID = server.isupport.get("BOUNCER_NETID");
+		let bouncerNetID = server.bouncerNetID;
 		if (bouncerNetID) {
 			bouncerNetwork = props.bouncerNetworks.get(bouncerNetID);
 		}