Update how nested perspectives are setup for collections

Nested Collections with namespaced models were receiving very odd defaults for the `as` option.  For instance,a nested collection for instances of SomeModule::Group was creating a Collection with `:somemodule::group` as the `as` option.  This makes defining a perspective that leverages the default `as` param rather cumbersome.  Additionally, because of the call to base_class in the calculation of the default for `as`, it was impossible to define a nested collection for a PORO with an associated persepctive.  I updated the calculation of the default to demodulize class names and to only call base_class when it is available.