Fix copy migration.

[ADDED]     Also log detailed errors.
[FIXED]     Create the cloud content directory if it doesn't exist yet.
[FIXED]     Same destination MOC after copy migration.
Rebuilding of the local cloud container.

[ADDED]     Support deletion of the cloud data on the device only (allowing it to be rebuilt from the iCloud data).
[IMPROVED]  More verbose error printing.
[IMPROVED]  Send willLoadStoreIsCloud to application when clearing the store so it knows the store is unavailable while it's being deleted too (in fact, whenever the PSC is cleared).
Improved store clearing on open error and do store reloading on import error.

[UPDATED]   Use clearStore to clear the PSC on error to make absolutely sure it's cleared.
[FIXED]     When a log import fails, reload the store to see if it's still viable to prevent the illusion that iCloud is still enabled and working while in reality it's broken.