Show overview of all added extensions and versions

Hi Guys,

thanks for providing a marketplace solution for closed environments!

It would be great if there was something like `code-marketplace list/overview` which returns an overview of extensions and their versions are on the marketplace. This would make it easier to clean up (i.e. remove old versions).

It could look something like this:
```
vadimcn.vscode-lldb
- 1.9.0
- 1.10.0
DavidAnson.vscode-markdownlint
- 0.54.0
- 0.55.0
... and so on.
```