SPDX standardizes how source code conveys its copyright and licensing information. See https://spdx.github.io/spdx-spec/1-rationale/ . SPDX tags are adopted in many large projects, including things like the Linux kernel.
This prevents libusb warnings from showing up even when the user is not using Bluetooth or USB passthrough, or the Wii U GC adapter.
This adds a USB passthrough setting to ConfigManager and everything needed for the UI to show and manage the whitelist properly.
