Please introduce a method to lock diagrams to prevent unwanted changes

[spainala]

Please introduce a method to lock nodes/connectors in a diagram. It is simple to select a node and mistakenly drag or move the diagram.

It would be really helpful to lock a diagram to prevent changes. If the diagram needs to be changed. Unlock the diagram. Make changes and then apply the lock to prevent further changes.

[JimTharioAmazon]

Changes:

• Add lock icon toggle to top-right of diagrams
• Store lock status per diagram in Settings table
• Disable dragging nodes on diagram surface when locked
• Disable diagram menu items when locked

These menu ids are disabled when a diagram is locked:

const menu_ids = ["diagram_manage_contents", "diagram_add_downstream", "diagram_add_upstream",
      "diagram_add_all_nodes", "nodes_align_vertical", "nodes_align_horizontal", "nodes_layout_vertical",
      "nodes_layout_horizontal", "nodes_layout_isolated", "diagram_remove_selected", "diagram_remove_diagram"];

[JimTharioAmazon]

Top left locked:

[JimTharioAmazon]

Disabled menu items when locked:

[JimTharioAmazon]

Locked diagrams still accept drag-n-drop nodes, so reopening to disable drop target when locked.