Allow the saving randomly generated maps with the .MAP extension.

[CCHyper]

Closes #256

This pull request allows the saving of randomly generated maps with the .MAP extension.

From the Random Map dialog, previewing the map from the selected settings and pressing "OK" will ask the user if they wish to save this map to a .MAP file.

The output format of this file is RAND_[date-time].MAP (for example, RAND_06-06-2021_21-34-26.MAP).

Example screenshot;