Added add, remove member methods to Group.
Added add, remove member methods to Group.

These methods will add or remove specified members from a Group. This should be
used with caution, as datasets previously obtained for a Group will not
automatically include the new member (or, conversely, reflect the removal of a
previously included member).

dotsdl/datreant,datreant/datreant,datreant/datreant.data,datreant/datreant.core,datreant/datreant,andreabedini/datreant,datreant/datreant.core