DDS12 — ObjectExtent and ObjectModifier can be removed

The ObjectExtent is a manager for a set objects. Basically it is a wrapper that offers functions to modify its contents and to create a sub-set based on on a user-defined function. The problem with using an Extent is that it overlaps with the get_objects method introduced in issue T_DLRL#3, and that it is not clear whether a new Extent should be allocated each time the user obtains it from the ObjectHome, or whether the existing Extent should be re-used and therefore its contents be overwritten with every update.
Furthermore, every application can easily write its own code that modifies every element in this sequence (no specialized ObjectModifier is required for that, a simple for-loop can do the trick), and similarly an application can also write code to filter each element and to store matching results in another sequence. Filtering and modifying objects like this are really business logic, and do not have to be part of a Middleware specification.

Proposed Resolution:

Remove the ObjectModifier and ObjectExtent from the specification. This saves two implied interfaces that are not required for most types of applications, but which can still be solved very well at application level. Replace the extent on the ObjectHome with a sequence of ObjectRoots.

see above