FInding nodelets by class name

[schmerl]

The way that nodelets are resolved is quite tricky. You can load them using the name of the class, but you don't know the name of the class until you parse the source, which we do after trying to find them. For the moment in:

What really needs to be done is to look through all the source files in info.targets to find which info.target defines the class in library.name or library.type, then add that target keyed by the type as well. This is needed because nodelets can be loaded into managers by their class name.

But probably the whole nodelet resolution architecture needs to be rethought.

[schmerl]

There is a workaround in: #509