rename libsundials_interface to libsundials_common

This is to avoid ambiguity with the upcoming debian libcasadi-sundials package (which contains the plugins)
create libcasadi-sundials-common package
remove some debian copywrites

these removals are all for files which are no longer distributed in the debian package
add CMAKE_SKIP_RPATH=ON for debian
add libcasadi_integrators to debian core packages
skip sqpmethod/stabilizedsqp tests if solvers aren't there

debian doesn't install these so the tests fail without this patch
add dummy snopt c++ library