Allow users to specify a grid on the map using the mouse
Many computations will be done on nodes of a grid that spans a specific area on the map. The user should be able to simply draw a boundary rectangle on the map using his mouse. The GUI should then fill the rectangle with a grid and allow the user to adjust the grid spacing.
The resulting grid must be added to the current project and persisted on disk (e.g. in a subfolder grids).