Add an option to use the default JetBrains icons

Great theme! It's awesome that you're working on a version for JetBrains IDEs, because they're really lacking truly polished color themes. A huge plus for the island theme support. However, I'm very used to PHPStorm's default file and folder icons and I'd really love to be able to stick with them while using the Vira theme for the rest of the IDE.