Enhance workspace command to include --exercise, --track, and --team

If any of these are passed, then print out the relevant path.

By default tracks and exercises go in the root of the workspace, but if you're part of a team, then there's a separate directory tree under `teams/$team`:

```
$WORKSPACE
├── go
│   └── hello-world
├── ruby
│   └── hello-world
└── teams
└── funfun
└── go
└── gigasecond
```