solvers-eiquadprog: Also tell the target about the include and link dirs

[pierrewillenbrockdfki]

This allows the cart_pos_ctrl_eiquadprog tutorial to build with separate_prefixes=true

@dmronga , the other option is to have the pkg-config query or, at least include_directories in tutorials/kuka_iiwa/CMakeLists.txt

[planthaber]

This PR solves basically the same issue as https://github.com/ARC-OPT/wbc/pull/33

[dmronga]

Thanks for your PR. I prefer this solution. I will close #33

[planthaber]

Looks like the "target_link_directories" command is not available on ubuntu 18.04