Simplify printing procedures

Simplify printing procedures

Use opencv's print() procedure in place of my own procedures to output
matrices and std::vectors.

Interestingly enough, operator<< does not work for matrices, when called
from my .cpp files in src/ subfolder of the optim module, although it
works when called from tests and stand-alone programs, compiled with
opencv. I think, this requires investigation and, maybe, bug report.