The addFrame returns now a bool which its false when the frame already
exists.

[unittest] Fixed precision comparison test.

[Python] Updating Python tests to corresponds to the API 

[Python] Updating Python tests to corresponds to the API ( e.g we add frames for every link and joint we encounter in urdf )

Topic/difference interpolate fix

[C++] The method forwardKinematics now selects by itself the section of the right DoFs over a full vector

Append cflags to the .pc file 

Topic/visuals without fcl

Add missing forward declaration.

Replace nbody to njoint and activate all collision pairs by default

Make coverage and cppcheck optional and dependant of the current branch