Clear play queue on login and logout

ui/src/layout/Logout.js

@@ -0,0 +1,15 @@
+import React, { useCallback } from 'react'
+import { useDispatch } from 'react-redux'
+import { Logout } from 'react-admin'
+import { clearQueue } from '../audioplayer'
+
+export default (props) => {
+  const dispatch = useDispatch()
+  const handleClick = useCallback(() => dispatch(clearQueue()), [dispatch])
+
+  return (
+    <span onClick={handleClick}>
+      <Logout {...props} />
+    </span>
+  )
+}