move nlopt and ipopt forward
up #407
 - fix option type for maxeval: it is an int
allow setting a bilinearform to zero which is equivalent to set the associated
algebraic representation to 0
up #407: update submodule nlopt
up #407 : cmake for nlopt
 - call autotools if necessary to generate c++ header file nlopt.hpp
 - do not use system nlopt anymore, it allows only for pointer functions
up #407 : use function object
 - allocate all big objects (mesh, space,...) in constructor
 - defie `operator()` member function with expected syntax by
 nlopt (`nlopt_func`)
 - use `std::ref` to avoid copying of functor
Merge branch 'develop' of https://github.com/feelpp/feelpp into develop