Motivation for this change

Even though it's old, Scala IDE 4.7.0 is newer than the version 4.4.1, which is currently available in nixpkgs, but broken.

This commit fixes the break and updates Scala IDE to its most recent version.

Things done

Unfortunately scala-ide is based on eclipse 4.7 (oxygen).
Thus is requires a java SDK 8 and GTK2.

The java SDK is easily overwritten. It would have been possible to have an override gtk3 = gtk2; as well, but I opted for the

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• 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 nixpkgs-review --run "nixpkgs-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.