Only connect to chat when authenticating in the first place

To avoid duplication of the connection, the chat socket is destroyed
upon logging out.

src/modules/chat.js

@@ -1,12 +1,16 @@
 const chat = {
   state: {
     messages: [],
-    channel: {state: ''}
+    channel: {state: ''},
+    socket: null
   },
   mutations: {
     setChannel (state, channel) {
       state.channel = channel
     },
+    setSocket (state, socket) {
+      state.socket = socket
+    },
     addMessage (state, message) {
       state.messages.push(message)
       state.messages = state.messages.slice(-19, 20)
@@ -16,8 +20,12 @@ const chat = {
     }
   },
   actions: {
+    disconnectFromChat (store) {
+      store.state.socket.disconnect()
+    },
     initializeChat (store, socket) {
       const channel = socket.channel('chat:public')
+      store.commit('setSocket', socket)
       channel.on('new_msg', (msg) => {
         store.commit('addMessage', msg)
       })