Add copper clearing feature.

[Juan Pablo Caram]

This might require first a tool to identify the different copper polygons.

[Juan Pablo Caram]

Done. Identifies polygons by subscribing a method to the event of click over the plot, then iterates over polygons until the point is found to be inside. Then runs clear_poly().

It still leaves a gap in the center of the polygon as a buffer of the same distance as earlier buffers yields a zero are polygon, but it can still generate a polygon with a smaller buffer length. Creating another issue for this (Issue #41).