Mac fixes and improvements to usability.

[FIXED]     Mac: Locking shouldn't unset the active user.
[IMPROVED]  Mac: Behavior of auto-completing site-name field improved.
[ADDED]     Mac: Alert when MP is incorrect when unlocking.
Update of iOS code for updated API of UbiquityStoreManager.

[UPDATED]   UbiquityStoreManager's new API uses cloudEnabled instead of iCloudEnabled.
Added a few missing resources.

[ADDED]     Mac: Missing menu icon.
[UPDATED]   Sketch source file for iOS app icon and Mac menu icon.