Feature: Selected objects are made a group in the window #40

Problem

• Groups exist only when the script builds them as ObjectGroup; components placed from the catalog can not be grouped
• Objects that belong together must be selected together again each time they are moved

Proposal

A selection of several objects becomes a group with one command. The new group behaves like a group from the script: it is selected, moved, rotated and hidden as one, and its parts can still be browsed. A group made in the window can be ungrouped again; both steps can be undone and appear in the exported script.

Tasks

• A selection of several objects becomes a group with one command
• The new group moves, rotates and hides as one, and its parts can be browsed
• A group made in the window can be ungrouped again
• Grouping and ungrouping are steps of the undo history
• export_script writes the group with its members

Notes

• Needs the issue "Feature: Several objects are selected at once"
• Checked on main: groups from the script are already shown and browsed
• Open question: may objects of different systems, or an object that is a member of several systems, be grouped?