Improve caching of group box information when creating content for Property Editor

[magnesj]

When the Property Editor is populated with widgets, the group bxes are reused based on name. This does not work well as the name of a group box can be the same for two different objects.

Possibly other members in this class could cause issues as they use the name of the item as key.

See std::map<QString, QPointer<QMinimizePanel>> m_groupBoxes; in cafPdmUiFormLayoutObjectEditor.h