update view_corr_mat in visualisation commands

[Islast]

The function view_corr_mat in visualisation_commands needs to be redesigned to plot matrices that are not saved as files.

[wingedRuslan]

Is this issue still relevant?

Right now view_corr_mat takes filename as an argument. Then corr_mat is loaded(numpy.loadtxt) from the file.
Would you like the function to take the corr_mat object as an argument instead of filename?

[Islast]

Ideally I would like the function to be such that one can pass a correlation matrix (say a numpy array or pandas dataframe) and plot that, or optionally pass a filename instead.

[Islast]

adressed in #108