Added deps command to resolve package dependencies without installing

I've created a `deps` command to resolve package dependencies and its versions.
It's useful for creating a `requirements.txt` file for later use with the `--no-deps` parameter.

The usage and the solution are very similar to the `install` command using the `--no-install` parameter, collecting `InstallRequirements` objects and printing the package and version information.

Tests are included.