Add cli command to clean up spaces

[kobergj]

When ocis crashes while a space is deleted, there is a possibility for parts of the space not being deleted. We need a small cli program that runs over the disc and removes all partly deleted spaces.

If it is not possible to identify broken spaces automatically, this command can also take a spaceID and remove all instances of it.

Make sure the cli removes all appearances of these space including:

• space index
• disk leftovers
• blobs
• ...