Hi Roger,
The Moodle 3.5 app currently supports fontawesome v4.7. So adding the propper HTML like: <i class="fa fa-address-book" aria-hidden="true"></i> should be enough to show the icons propperly. There are some parts where html is not allowed (i.e activity titles) but ou would see the icons in any platform. If you want to add styles to that icons you should use inline styles or remote themes.
I hope this clarifies your doubt!
Cheers,
Pau