NMF: Added flag for controlling output to std::cout, reduced test execution time.

By default, NMF no longer prints output to std::cout, but can be configured to do so.
Execution times for tests exceeded 25 minutes on an old Nvidia GT 9600, thus running into time-outs.
Maximum number of iterations is now reduced from 10k to 5k and the size of the largest test problem slightly reduced,
so tests should stay within the time limit.