Add one repo task - please review

This is one of the repository tasks that a CI (continuous integration) system will need to compile and run tests against a project checked out from source.

This task (as described in the documentation) will download a maven jar and create the wiring for direct dependencies only.  it downloads it and renames it to the Ceylon format in the Ceylon cache -- just as if it was downloaded from Herd.

A developer would need to define all jars in the build system, but only define the top-level in module.ceylon.  This approach takes care of infinite recursion and dependencies that are not really required.

Ultimately, this task would be a subtask of a task that reads module dependencies form module.ceylon and verifies / downloads.

My code is not as well-organized and well-formatted as yours :), so please advise - 
- should it be separate module, project etc.?
- Since it involves network traffic, what kind of test would be enough. There is simple test in run().

Todo - implement javadocs, sources etc., cleanup pom and parent files.