Posibility print some layers in color and others in black

[ggsalas]

Qcad3 have the feature to print in 3 ways: color, grey and black.

The missing feature is select some layers to preserve the original color in the black mode of print.

I have added this request in bugtracker http://www.ribbonsoft.com/bugtracker/index.php?do=details&task_id=651