UI improvements & security.

[ADDED]     Settings for remembering and storing the master password.
[ADDED]     KeyChain used to store master password & hash.
[IMPROVED]  Remember whether help is hidden.
[FIXED]     Making passwords stored.
[ADDED]     Generated password counter. Edit stored passwords.
[IMPROVED]  UI prettier and better documented.
[ADDED]     Warnings when changing a site's password.

OnePassword/OPAppDelegate.h

@@ -16,6 +16,7 @@
 @property (strong, nonatomic) NSString *keyPhrase;
 
 + (OPAppDelegate *)get;
++ (NSManagedObjectContext *)managedObjectContext;
 
 - (void)saveContext;
 - (NSURL *)applicationDocumentsDirectory;