Reduce verbosity of ASCII dependency tree/graph by eliminating repetition

[winitzki]

Currently, for each dependency the entire subtree is printed every time the dependency is encountered while walking the graph. This makes the output of sbt dependencyTree and sbt dependencyGraph extremely verbose and very hard to use in practice.

It is probably not difficult to add an option that will avoid printing any subtree that has been already printed. The subtree that was already printed could be marked with a * or something like that.

I tried to look at the source code of the plugin but could not see an obvious place where to do this, but perhaps it's obvious for the plugin's author. Please consider adding this as an option or as a default behavior. Thank you for a great plugin! We are using it for all our projects whenever we need to examine dependencies. I just wish it were easier to use, and I think this feature would make a big difference.