ModuleInfo: add a loadDelegateClass() method

This makes it easier to more consistently and safely obtain the Class<?>
object associated with the meat of the module being described.

Previously, you could call getDelegateClassName() but then there was no
safe way, in general, to load that class in all situations

Previously, you could call getDelegateClassName() but then there was
no safe way, in general, to load that class in all situations.
AbstractModuleItem: lean on loadDelegateClass()

Now that ModuleInfo has a handy method for loading its module's delegate
class, we can use it directly rather than relying on the unsafe and
problematic usage of the ClassUtils#loadClass method.
Merge pull request #75 from scijava/load-delegate-class

Add an API for ModuleInfos to load their delegate class