finished implementation of sensitivity propagation techniques for ERK methods
improved speed of ERK methods forward sensitivity propagation
added AD support for forward and backward derivatives with matrix seeds
improved forward sensitivity propagation in ERK methods using the new AD functionality
improved forward-over-backward second order sensitivity propagation in ERK methods using the new AD functionality
added custom functionionality for the new three-sweeps-propagation approach to make it at least competitive with forward-over-backward, currently lacking specific AD functionality for the operators involved
added symmetric AD functionality, fixed ADbackward, enabled stacking of variables
Merge branch 'master' of github.com:rienq/acado into stable

Conflicts:
	examples/basic_data_structures/function/symbolic_differentiation3.cpp
	external_packages/src/acado_gnuplot/gnuplot_window.cpp
	include/acado/utils/acado_types.hpp
	src/symbolic_operator/projection.cpp
resolved merge conflicts
Merge branch 'master' of github.com:mvukov/acado
fixed warning in function.cpp
fixed warning in three-sweeps integrator
minor reformatting
minor reformatting
moved functionality of clearing all static counters, not limited to MATLAB interface anymore
removed the dimension argument from function 'returnLowerTriangular'
modified function.cpp
merge with Boris
corrected doc of ubAValues
fixed minor bug when having variable state bounds in N2 condensing