title: Add external javascript library to odoo 12
body: <p>Hello i'm new to odoo and i'm using version 12, i want to add an external javascript library which is loading.io <a href="https://loading.io/progress/" rel="nofollow noreferrer">https://loading.io/progress/</a>.</p>
  <p>I don't know how to add it because i saw that it is not possible to use a cdn.</p>
  <p>Any help or hint will be appreciated and thanks in advance.</p>