Dissmisable alerts

[fettuccinae]

Problem

The alert wasnt dismissable and it felt like it reflected the status of user's last.fm connection.
https://tickets.metabrainz.org/browse/LB-1728

Solution

Added a button which onclick disables the visibility of alert.

[MonkeyDo]

I think that is a good idea, thanks for opening a PR !

There is a simpler way to dismiss alerts. You don't need a stats variable, just the close button with no onClick param, and a few relevant css classes: you can follow the steps in
https://getbootstrap.com/docs/4.0/components/alerts/#dismissing

The button html content is very similar to what you currently have:

<button type="button" class="close" data-dismiss="alert" aria-label="Close">
   <span aria-hidden="true">&times;</span>
 </button>