CAD - Make it possible to select an individual polygon if you have multiple polygons in 1 SD object

Currently, CAD files can be imported to Qimera and they are converted to .sd format.  If these .sd files contain only a single polygon, they can then be used as a spatial selection area.  This improvement would extend this behavior to CAD files that have multiple polygons, and the user would be able to choose which polygon in the resulting .sd file is to be used for a particular selection.

This case is closely related to another case in which the ability to use ALL the selections for a filtering operation is requested:  https://jira.qps.nl/browse/FQM-331