switch to simple new group::update call with dict as argument
This change fixes as well a bug in install::xml::action::set-join-policy since group::get returns a member "text" which is not accepted by group::update.
Provide an optional object_id which can be used to register message keys that will be bound to the lifecycle of an acs-object. When the object is deleted, so will the message key. This is useful for groups that automatically define a message key for their pretty name. Tcl api was already aware of this and would cleanup such message keys, but other idioms e.g. stored procedures used to delete groups would leave leftovers behind. These can become relatively numerous on group-intensive systems such as LEARN.
Other future usages for this new feature might be the automatic localization of xowiki FormPage properties.