Commands for local publish/install

[simonegaffurini]

It should be possible to publish and install a package without connection to a registry.
Implement:

• pack
  will generate a TRM artifact and save it to local disk
• import
  will let you pick a file from local disk and import it into an SAP system

Notes:
the registry name of the artifact generated has to be discussed: technically, it's not a package from any registry so it might be best to just exclude it from the installed packages list (maybe add a flag to the manifest).