Draft OCA/cs

Opening
This function imports OCA/GCAD files. The OCA file format is community effort to create a free, simple and open CAD file format. OCA is largely based on the GCAD file format generated from gCAD3D. Both formats can be imported in FreeCAD, and the OCA files exported by FreeCAD can be opened in gCAD3D.

The following OCA objects get imported at the moment:
 * Lines
 * Arcs and Circles
 * Closed areas

Importing
Works the same way as opening but creates the objects in the active document instead of creating a new one.

Exporting
Objects that can be exported at the moment:
 * Lines and wires (polylines)
 * Arcs and circles
 * Faces

Preferences
The following parameters can be specified in the Draft Preferences tab (menu Edit -> Preferences -> Draft):
 * Import closed areas or not