Review definition and meaning of "Group"

**Description**

The current implementation of "Group" assumes it to represent a value that considers endianess of multiple MAUs.
Introducing this and enabling editing of groups raised a couple of discussions that need to be continued and resolved after #108 got merged which adds editing memory as per the current approach.

* Is "Group" really still the right name for it?
* Should "Group" be just a visual grouping or really come with a specific meaning like it does today?
* Should the Group concept be replaced by a new concept that explicitly states the meaning of a grouping. Could be based on primitive data types of a debugged application. For example "char", "short", "long", "float", "double", etc for a C/C++ debugger.
* This approach could be expanded to contributions from debug adapters.

User feedback from a release with #108 could help to steer such discussions.

**Additional information**

People involved in initial discussions were @colin-grant-work , @planger , myself.