Define ComponentPlugin API type

Just writing down how I think plugins should get registered with the system. Was thinking it'd be nice to do the event thing as a plugin.
Note that being "statically-linked" as I described above does not prevent the plugins from being in separate processes for micro-kernely goodness, if that is what we want.  But it does enable them to be packaged into a single busybox binary (which I think is what Clayton wants).