feat: Save feature

[Alystrasz]

Reworks the way SERE saves graphes:

• Display graph file path as window title;
  • An asterisk is displayed before file path if graph has been modified in the node editor and not exported to disk;
• Split the "Save Graph" into two different options:
  • "Save" exports graph to the current selected path (can also be triggered with the Ctrl+S keyboard shortcut);
  • "Save as" opens the file explorer to select a destination.

Currently, the "unsaved" status is set using the nodes count, which means it's not triggered if a node status changes (e.g. updated pin value).

[RoyalBlue1]

Other than the HWND thing changes look good