titles for histograms.

When several cathegories (e.g. licit, spoof) are need for each system
without evaluation scores.

It is used to define custom legends for dev, eval plots

Use same legend for dev and eval hist when the number of legends is
equal to the number of systems. It is still possible to change the
legends of individual histograms by passing 2 * #system legends.

Remove threshod vline form histogram plots

plots

Before only one title could be changed even when two plots where in the
figure and title was augmented with (development/evaluation). Now the
titles can be entirely defined.

Modify the display of histograms: now can use subplots to display several histograms on one page, can no longer display both dev and eval histo at the same time, can control the number of columns in the legend

Add min-far-value option, rename -l (already used) to -Z, change the way linestyles are handled and make use of them optional