[hotfix] Changed from assignation to initialization for a matrix in symmetric3 that causes computations errors with ubuntu 14.04 in release mode.

[C++]{Minor] Changed the name of the method to access the segment of a given vector. The length of the returned segment depends on the dof of the joint(size NQ or NV)

[C++][Major] Reorganized the methods to acces segments of fixed size (one for NQ, one for NV) from joints indexes

[C++][Major] Added JointModelDense and JointDataDense. Both templated by the dimension of configuration space and tangential space. Each joint can be converted to a Dense one

[Major][C++] Renamed macro for spatial traits : 2 cases -> use in templated/not templated classes to avoid polluting warnings. Following these naming could avoid multiple definitions of macro SE3_JOINT_TYPEDEF

[C++][Major] MotionRevolute is now CRTP. Moved out of struct JointRevolute to solve namespace problems

[Major] BiasZero is now a MotionBase (CRTP), implemented in jointrevolute. Switch in other joints to come

[Major] spatial class SE3 is now CRTP. Move traits class in spatial/fwd.h as it is now used in spatial classes and joint-base

[Python] force the computations of all coefficient in the mass matrix, in the binding of computeAllTerms.

  - This is necessary to build with older compiler versions.
  - The keyword typename must only be used in template declarations
    and definitions and only in contexts in which dependent names can
    be used. This excludes explicit specialization declarations and
    explicit instantiation declarations (until C++11).