Fix error in CustomRegistrars; return a function when
creating general-purpose registration code for
Angular built-ins which follow the normal pattern
(directives, controllers, services...)
WTD-518.
Handle the iteration over extensions which have a
custom registration mechanism (directives, services)
at the same level that general registration is handled.
WTD-518.
Continue implementation of registration phase of framework layer.
Begin adding some custom registration behavior for specific
Angular concepts, such as services and directives. WTD-518.