#188 Add a "node" for Crux in ProteomeDiscoverer

[William S Noble]

This is something that Mike MacCoss recommended to increase Crux's visibility. I have not yet investigated the details, but apparently they have an API and an SDK that allows tools to be incorporated into the commercial ProteomeDiscoverer software. Lukas worked with them to get Percolator in there. We might do this for Tide, Barista, etc. (or maybe Crux in general, depending on how this works).