Added drawCircle function to Graphics module for Point2d
Accuracy fixes for the Cone object
Reduced header dependencies in Geometry module

Concerned implementation files are ConvexHull.cpp, BBox.cpp, Polygon.cpp
Removed type checking in cross function in Geometry module:

Integral types are allowed to compute the cross function.
Reviewed implementation of Triangle and Quad

- The vertices of the triangle/quad are not reordered in a CCW manner
anymore during the construction.
- Added default constructor to triangle
Minimized header dependencies in LineSegment.cpp
Updated DO/Geometry/Objects.hpp
Changed index names in point-in-polygon algorithm

This is subjective but I believe it makes code more readable
Implementation of ellipse intersections undergoing changes

- The  computation of the area of intersecting ellipses is still buggy
but goes in the right track. Work in progress.
- Added several unit tests for the geometry module.
Added other useful 3D geometric objects.
Started implementation of simple geometric kernels.

- This is only at the stage of vague idea. This might come in handy
later.