[InverseDynamics] Support for Jacobians & derivatives

This change adds support for calculating Jacobians and
dot(Jacobian)*u terms, along with the required support for
the 3xN matrices in the standalone math library.
It also adds functions to compute kinematics only (position, velocity, accel).
To facilitate tests, the Cl also adds a RandomTreeCreator to create
randomized multibody trees.
Thanks to Thomas Buschmann for this contribution!

Extras/InverseDynamics/IDRandomUtil.hpp

@@ -2,8 +2,10 @@
 #define ID_RANDOM_UTIL_HPP_
 #include "BulletInverseDynamics/IDConfig.hpp"
 namespace btInverseDynamics {
-/// seed random number generator
+/// seed random number generator using time()
 void randomInit();
+/// seed random number generator with identical value to get repeatable results
+void randomInit(unsigned seed);
 /// Generate (not quite) uniformly distributed random integers in [low, high]
 /// Note: this is a low-quality implementation using only rand(), as
 /// C++11 <random> is not supported in bullet.