Added method to the Module base class in order to fascilitate package  development with dependent packages.
Added method to the Module base class in order to fascilitate package 
development with dependent packages.

Affected classes:
Module

New methods:
Module::get_instance_of_type(self, ident, name, ns='')

Details:
get_instance_of_type(...)
Queries the module registry at:
core.modules.module_registry

for a module in a different package.  This method essentially wraps the 
call:
core.modules.module_registry.get_module_by_name(..)

to ease the development of new packages.  In this way, the developer 
need not be concerned with the functionality of the module registry 
except for creating typed input/output ports.



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