WebHID does not work with Chromium when installed as snap package

[dlech]

Similar to #428, but for WebHID instead of WebUSB.

The firmware updater on the EV3 uses HID over USB, so the only way we can access it from a web app is via WebHID (WebUSB intentionally blocks HID devices from being used).

Unfortunately, there isn't an easy workaround that I could find for connecting the "hidraw" interface of the snap. The problem is there is nothing that provides a slot to connect it to.

Some relevant discussions:

• https://forum.snapcraft.io/t/the-hidraw-interface/7837
• https://forum.snapcraft.io/t/interface-request-hidraw-equivalent-of-raw-usb/15082
• https://forum.snapcraft.io/t/how-do-i-utilize-the-hidraw-plug-on-a-pi-running-ubuntu-core-18/11940

So the best we can probably do for now is add something in the error message to let people know what is going on when it fails.