Investigate whether user-select: none is still required in paper-tabs

[arthurevans]

I think the paper-tab content is no longer selectable by default, so we should be able to remove the user-select rules here:

  #tabs {
    width: 100%;
    margin: 0;
    -webkit-user-select: none;
    -moz-user-select: none;
    -ms-user-select: none;
    user-select: none;
    text-transform: uppercase;
  }

But we should verify on all browsers before dropping this.