Remove cout in favor of MsgStream

McEventCollectionHelper used cout statements to issue warnings that a pile-up type was unknown. This polluted log files e.g. when running FastChain_tf.py with no input min-bias HITS.

The changes here take all cout statements in the McEventCollectionHelper class and replace them with MsgStream. All clients of McEventCollectionHelper have also been updated to reflect the changes.

Output warnings now suppressed by message limits.