Repository.Token() generates a base64-encoded token that can
be stored in password manager that fully describes repository connection
information (blob.ConnectionInfo) and optionally a password.
Use `kopia repo status -t` to print the token.
Use `kopia repo status -t -s` to print the token that also includes
repository password.
Use `kopia repo connect from-config --token T` to reconnect using the
token.
Also introduced strongly typed content.ID and manifest.ID (instead of string)
This aligns identifiers across all layers of repository:
blob.ID
content.ID
object.ID
manifest.ID
This updates the terminology everywhere - blocks become blobs and
`storage.Storage` becomes `blob.Storage`.
Also introduced blob.ID which is a specialized string type, that's
different from CABS block ID.
Also renamed CLI subcommands from `kopia storage` to `kopia blob`.
While at it introduced `block.ErrBlockNotFound` and
`object.ErrObjectNotFound` that do not leak from lower layers.
