[TD]Refactor Dimensions for 3d upgrade

- separate validation, geometry and reference handling into
  individual files
- improve 3d reference geometry handling
- eliminate duplicate dim creation code

- add Dimension reference repair dialog

- Refactor formatting out of DrawViewDimension

- move dimension repaint control to ViewProvider

src/Mod/TechDraw/App/DrawUtil.cpp

@@ -46,6 +46,7 @@
 #include <BRepLProp_SLProps.hxx>
 #include <BRepTools.hxx>
 #include <GCPnts_AbscissaPoint.hxx>
+#include <GeomAPI_ExtremaCurveCurve.hxx>
 #include <gp_Ax3.hxx>
 #include <gp_Dir.hxx>
 #include <gp_Elips.hxx>
@@ -345,6 +346,25 @@ std::pair<Base::Vector3d, Base::Vector3d> DrawUtil::boxIntersect2d(Base::Vector3
     return result;
 }
 
+//find the apparent intersection of 2 3d curves. We are only interested in curves that are lines, so we will have either 0 or 1
+//apparent intersection.  The intersection is "apparent" because the curve's progenator is a trimmed curve (line segment)
+bool DrawUtil::apparentIntersection(const Handle(Geom_Curve) curve1,
+                                    const Handle(Geom_Curve) curve2,
+                                    Base::Vector3d& result)
+{
+    GeomAPI_ExtremaCurveCurve intersector(curve1, curve2);
+    if (intersector.NbExtrema() == 0 ||
+        intersector.LowerDistance() > EWTOLERANCE ) {
+        //no intersection
+        return false;
+    }
+    //for our purposes, only one intersection point is required.
+    gp_Pnt p1, p2;
+    intersector.Points(1, p1, p2);
+    result = toVector3d(p1);
+    return true;
+}
+
 Base::Vector3d DrawUtil::vertex2Vector(const TopoDS_Vertex& v)
 {
     gp_Pnt gp  = BRep_Tool::Pnt(v);