Dialog to handle import of unmatched layers from CADSTAR

Adds a dialog to allow the user to remap unmatched layers when importing a CADSTAR PCB. Partially fixes #5316 (closed)

This is necessary for importing older CADSTAR designs where the silkscreen, fabrication, assembly and glue spot layers were all classed as a "non-electrical" layer without any other distinction between then (except the name). A good example of such a board is here: https://raw.githubusercontent.com/marciomenezesjr/subspy/57d9b5adf91bd49b95f64098619f40dd1e71852e/reference/CC1150EM_Reference_Design_1_2/CC1150EM_0_2.cpa