Add option to list only project modules

[LukaJCB]

I think it'd be a very useful option to filter out all libraryDependencies and just show all the sbt subprojects/modules.

[udalrich]

Similarly, filtering the modules to a specific group would be useful. In mvn, one can do mvn dependency:tree -Dincludes=*akka* and only see the Akka dependencies (and the path to those).