Updated constants to handle different labels not only 'feature' and 'story'.
Updated pytest_plugins.py with features_label_type, stories_label_type and label mark.
Updated utils.py with get_marker_that_starts_with method to provide all labels through labels_of method and added LabelsList class with rules for list comparison.
Updated test_labels.py to use hamcrest matchers and new test for labels was added.