Allow component plane titles to optionally be interpreted as LaTeX

[willfurnass]

Noticed the following in som/som_show.m:

% Set text property 'interp' to 'none' in title texts

set(h_label,'interpreter','none');

Would be nice if could switch between standard text interpretation and LaTeX interpretation for component subplot titles. Made a start on this here but having problems with keyword argument parsing - any pointers gratefully received.