Extend Core API to better model life of an HDD in Dmedia

[Jason Gerard DeRose]

Currently our Core API only has 2 rather crude methods for dealing with the HDD lifecycle:

Core.add_filestore(parentdir) - creates file-store if it doesn't already exist, adds into the pool of currently connected file-stores

Core.remove_filestore(parentdir) - remove the file-store from pool of currently "connected" file-stores.

Plus we have a hacky mess for how deal with the "default file-store", which will be either /home or /home/username. We need finer-grained API that better models the life of an HDD in Dmedia, and I'm proposing something like this:

Core.create_filestore(parentdir, label) - error if file-store already exists. This is where we want to walk the user through labelling their HDD so the physical/written label matches what Dmedia has in CouchDB.

Core.connect_filestore(parentdir, store_id) - error if file-store doesn't exist or doesn't have the expected store_id. Adds to pool of currently connected file-stores, in other words the HDD that Dmedia will look for files on. We should call FileStore.purge_tmp() here, and then immediately run a quick-scan on the drive (in either a background thread or background process).

Core.disconnect_filestore(parentdir) - remove file-store from connected pool. This will usually be called in response to an event from UDisks.

Core.downgrade_filestore(store_id) - tell Dmedia that it should not count on any copies in this file-store. It will update all files to have {"copies": 0}, which will trigger Dmedia to create additional copies if needed. The file-store may or not be connected. If connected, this store can be used as a source for creating additional copies.

Core.purge_filestore(store_id) - tell Dmedia not to count on any copies in this filestore, and not to track them at all. It will update all files completely removing store_id from doc.stored. The file-store may or not be connected.