add method to safely print counters

For debugging it is often useful to check various cutflow entries (counters) by hand. However, in an interactive shell this is somewhat messy and unsafe (or cumbersome) as TQSampleFolder::getCounter returns a pointer which is a nullptr if no valid paths and/or counter names are given. Also getCounter(...)->print() inherently leaks memory. The clean way is to store the pointer and only print in a second command, however, for quick checks this is annoying.

Let's get a simple printCounter method into TQSampleFolder that wrapps the required steps