Upgrade to FontAwesome 5

Currently used FontAwesome 4.7.0 is outdated and not developed anymore (stopped in 2017).
So it could be a good step to upgrade to FontAwesome 5 (currently it is 5.13.0).

Pros:
1) Actual updated and actively developed font version.
2) 1588 free icons vs ~675 in version 4.7.0.
3) New brand icons included.
4) Special backward compatibility layer allows to keep all FontAwesome 4 references and syntax with minimal style changes. Also applies to extensions and custom styles.
5) Minor: possibility to use phpBB 3 with styles using paid FontAwesome plans for ones who wish that.

Cons:
1) Some icons used with FontAwesome 4 are available in FontAwesome 5 only in bold font type.