Merge feature and task factory with entity factory.

      * include/sot-core/additional-functions.h,
      * include/sot-core/factory.h,
      * include/sot-core/op-point-modifier.h,
      * src/CMakeLists.txt,
      * src/factory/additional-functions.cpp,
      * src/factory/factory.cpp,
      * src/feature/feature-1d.cpp,
      * src/feature/feature-generic.cpp,
      * src/feature/feature-joint-limits.cpp,
      * src/feature/feature-line-distance.cpp,
      * src/feature/feature-point6d-relative.cpp,
      * src/feature/feature-point6d.cpp,
      * src/feature/feature-task.cpp,
      * src/feature/feature-vector3.cpp,
      * src/feature/feature-visual-point.cpp,
      * src/matrix/fir-filter.cpp,
      * src/task/constraint.cpp,
      * src/task/task-conti.cpp,
      * src/task/task-pd.cpp,
      * src/task/task-unilateral.cpp,
      * src/task/task.cpp,
      * unitTesting/CMakeLists.txt.