Added quadrupedal walking benchmark in c++

This PR includes the c++ benchmark of the quadrupedal walking #261 (closed). The main purpose of this benchmark is to start debugging #250 (closed) #256 (closed). @proyan could you start to work on issue #250 (closed)?

Additionally, it includes other changed in the API based on shared_ptrs (with this we complete the !245 (merged)). Finally, this PR adds missing registration of shared pointers needed in the Python bindings (reported in #266 (closed)).