interface for inclusion of 3rd party content in
Typically, if the serverplugin type allows composition of lookup from
multiple sources, it will make a layer location public where 3rd parties
will register implementations of this interface.
implementations will be asked to create their additional project lookup based on the baseContext
passed as parameter. The content of baseLookup is undefined on this level, is a contract
of the actual serverplugin type. Each implementation is only asked once for it's lookup
for a given platform instance at the time when platform's lookup is being created.
baseContext - implementation shall decide what to return for a given platform instance based on context
a Lookup instance that is to be added to the platform's lookup, never null.