Added treeview with history to group_edit

Implementace/controllers/distribution_overview_controller.py

Implementace/controllers/group_edit_controller.py

Implementace/controllers/mainwindow_controller.py

Implementace/controllers/member_overview.py

Implementace/database.py

Implementace/model/distribution.py

Implementace/model/group.py

Implementace/model/member.py

Implementace/utils/qtmodels/distributions_tree_model.py

Implementace/windows/groupedit.py

Implementace/windows/qt/groupedit.ui