FontAwesome icon issues in admin area

[N8Solutions]

@hexplor I have come across an issue with a few icons in the admin area not displaying properly after installing J2Store. It happened a while ago but I never took the time to look into it until now. I opened a pull request for you to look at. It updates the problematic icons so they are more compatible with FA5.

It appears to have something to do with J2Store but I don't know why, and only a few icons are affected, which are the ones I fixed in the PR. The exception being the "Branding" particle because the fa and fa-fw classes seem to be added differently as they aren't hard coded into the particle.

https://github.com/gantry/gantry5/pull/3193

Please let me know if you have any questions.