The Wait() function will return a null TOOL_EVENT when the tool
stack is shutting down, so we can't just always pass the event,
instead we must check for null and end the looping if a null
event appears.
This uncovered a memory corruption bug in MODULE's move operator,
several bugs in MODULE's move and copy constructors, and a bug in
BOARD's GetItem() call.
It also bumps the file format for saving/restoring groups inside
footprints.
Also simplifies groups so that other areas of code that have to know
about them at least don't have to know as much. One of the simplifications
is to not worry so much about empty groups until save time; others are in
the access logic to parent groups.
Also simplifies user model slightly by removing Merge and Flatten
(which are just ungroup/group and ungroup/ungroup/.../group).
Also allows multiple groups to have the same name. This is useful when
using groups for a classification system.
Fixes https://gitlab.com/kicad/code/kicad/issues/5788
ADDED memberOf() function for DRC rule expressions.
Also fixes a bug in several of the pickers where the event wasn't
being correctly passed.
Fixes https://gitlab.com/kicad/code/kicad/issues/5647
Ian McInerney
Seth Hillbrand
Jeff Young