Draft - Allow to export Drawing pages to DXF - fixes #1686

* Uses DXF algos of the Drawing module instead of the Draft dxf library
* Uses a DXF template with the same name as the SVG template, if existing
* Only Draft, Arch, Part and Annotation views are currently supported
* Drawing module's projectToDXF() now returns only a fragment instead of a full DXF file
improve sweep output
support for point, vertex and object cache
use rounded floats if they safe digits

Sometimes the floats seems to be rounded to twelve decimal
places. we round them if it allows so safe digigts.
round angles
check for arc and do not explode edges
format radius
load only MODELING module