More robust migration.

[FIXED]     Better recovery from failure to migrate local store.
[FIXED]     Ability to migrate outdated local store models.
Log VC, iCloud toggling, iOS 7 fixes.

[UPDATED]   Show users and sites in cloud stores of log VC.
[ADDED]     Ability to turn off iCloud if corruption happens.
[ADDED]     When switching iCloud on/off, provide user the option to migrate his current sites.
[ADDED]     Ability to get to settings & logs from unlock VC.