Whitlisted DL kara

The idea

Add a way to download only specific karas.

• Add a dry-update command which only add new karas' metadata from kurisu and don't delete anything
• Do the same thing with a dry-import command to update favorite lists from kurisu (or do this with the dry-update?)
• Add a whitelist argument to the udapte command

Usage

The new lkt commands may look like:

lkt adm dry-update        # Download the metadatas
lkt adm update plt @Sting # Download only karas from Sting's favorites
lkt adm update 5819       # Only download the kara with a specific ID