Redirections of type implementations

Each (non-data) dynamic has an application associated with it. This application
provides an implementation for that dynamic. For the time being this
application has been fixed to the application that created the dynamic.

This may change in the future. For example if another application also
provides the implementation and can be shared by dynamics, then the 
amount of references can be reduced to that application.

It is pointless to associate an application with a data-dynamic because
its contents can only be used if the external type matches the specified
pattern in the application reading that dynamic.

Reading a dynamic:
- after a dynamic has been correctly type checked, the implementation
  chosen for that dynamic *overrides* a implementation provided by 
  the application of the dynamic. 
 
  It should be noted that in case of a datadynamic, no implementation
  will be provided.