Interface for plugins to trigger hardware detect

[rpavlik]

Sometimes SDKs can tell us when a new device shows up. While we could probably just add the device then, we might get into threading issues depending on a number of factors. An easy way of handling this would be to be able to tell the server from the plugin, "please hardware detect when you get a chance". Related to #153 in this way.

[rpavlik]

And this basically is just wiring the API parts, since there is an internal API for triggering hardware detect of course.