Cosmetic change: fix doxygen documentation

  - notify copyright outside doxygen,
  - remove obsolete tags.
Add missing "inline" in configuration.hh.
Simplify integration on angular velocity from quaternion.
Try to keep norm of quaternion close to zero when integrating.
Rename private method

  Joint::computePosition -> Joint::recursiveComputePosition.
Make Joint::computePosition public and provide reference to result as parameter.
Add an inline toEigen function for matrix3_t
Update to new version of fcl

  - move fcl forward declarations to fcl,
  - create doxygen link to fcl documentation.