add support for multi-module dependencies listing and other top-of-tree calculations on sub-modules

Currently, the dependencies file only contains the dependencies in the current project. However, in cases where we're releasing a multi-module project all at one go, it would be nice to support collecting all dependencies from sub-modules, winnowing out the inter-module dependencies, and using that collection for generating the dependencies file instead of only those dependencies of the current project.

It also may make more sense in these cases to mimic the assembly plugin's runOnlyAtExecutionRoot flag, and only process the remote resources once for a project tree.