font-awesome_4: Readd, font-awesome_5: 5.9.0 -> 5.10.0

[JohnAZoidberg]

Motivation for this change

Version 5 is incompatible for some icons, so projects that depend on it
need to actively convert the symbols, see:
greshake/i3status-rust#130

Reintroducing the old version lets us use those programs that haven't
been updated.

Was removed in 0a393f5

cc @Mic92 and @baldo

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nix-review --run "nix-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

---

[peterhoeg]

The "nicer" way to solve this is a generic build function for font awesome that takes the version and sha256 as parameters (refer to to unifi or vala for some examples). Might also be good with a comment that explains why we have the _4 version.

[Mic92]

Can you add a concrete example, why we have this package? Then we can reevaluate in future if we still need the old version.

[JohnAZoidberg]

What about this? :)
Took the opportunity to upgrade to the latest v5 release from earlier today.