Classify without labels, restrict training set

[fahrenfort]

Two updates:

• It is now possible to plot the outcome of the classifier without labels in the test set, i.e. by plotting the probability each time point is classified as the first class in the class definition. Use cfg.compute_performance = 'no';
• It is is now possible to restrict the number of trials in the train set (e.g. when comparing to another analysis with fewer trials in the train set). Use cfg.restrict_trainset = [int]; Also other minor fixes, e.g. when plotting symmetrical temporal generalization.