Minor fixes (check for net codes size for ratsnest, cursor coordinates are not always shown as if the cursor was snapped).

Screen size is saved in VECTOR2I instead of VECTOR2D.

Removed EDIT_CONSTRAINT::Update() - replaced with resetting constraints.
EDIT_CONSTRAINT is stored in EDIT_POIN using boost::shared_ptr instead of pointer.
Added EDIT_LINE::GetEnd() & GetOrigin(). Overridden ApplyConstraint() for EDIT_LINE.
Side EDIT_POINTS for zones are drawn as circles.

Switched order of EDIT_POINTs for DIMENSION, so in case when feature lines are of 0 length, then still can be stretched.

Dimensions have EDIT_POINTs.
Different handling of 45 degree mode in POINT_EDITOR.

Workarounded SWIG problems (does not support nested C++ classes, more on the subject: http://www.swig.org/Doc1.3/SWIGPlus.html#SWIGPlus_nested_classes).

Added a few settings to make the layer settings more similar to KiCad defaults (moved vias to VIA_THROUGH_VISIBLE, added a few rules for required layers).

Added POINT_EDITOR::isModified().