Improve the plot generation in simulate_mimo.py
Rename simple_maxsinr.py and add quantization code
Allow the Nt and Nr arguments to be int values

Allow the Nt and Nr arguments to the init_from_channel_matrix method of
the MultiUserChannelMatrix class to be int values.
Fix some pylint warnings
Refactoring of the code in mimo.py

New MisoBase class as well as the _calc_precoder and
_calc_receive_filter methods in all class where this is possible.