Make Firmware Ninja's auto-detection also consider user-supplied board descriptions

[fuzyll]

What is the feature you'd like to have?
Right now, Firmware Ninja's board auto-detection only works with bundled board descriptions. We should also make it work with ones provided by the user.

Is your feature request related to a problem?
Users may have access to board descriptions that we do not. They may also be unwilling or unable to contribute those back to us. It'd be nice if they could use all of the features of Firmware Ninja regardless.