added NSNotifications for outside classes

Allow other classes to get notifications. For example:

```
- (void)viewDidLoad {
    [super viewDidLoad];
    // Attach notification controllers
    
    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(receiveTestNotification:)
                                                 name:@"MyBeatDidConnectPeripheral"
                                               object:nil];
    
    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(receiveTestNotification:)
                                                 name:@"MyBeatDidDisconnectPeripheral"
                                               object:nil];
    
    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(receiveTestNotification:)
                                                 name:@"MyBeatDidUpdateState"
                                               object:nil];   
}

- (void)receiveTestNotification:(NSNotification *)notification {
   
    if ([[notification name] isEqualToString:@"MyBeatDidConnectPeripheral"]) {
        
        NSLog (@"Successfully received the MyBeatDidConnectPeripheral notification!");
        NSDictionary *userInfo = notification.userInfo;
        CBPeripheral *myPeripheral = [userInfo objectForKey:@"peripheral"];
        NSLog(@"peripheral id: %@", [myPeripheral UUID]);
        
    } else if ([[notification name] isEqualToString:@"MyBeatDidDisconnectPeripheral"]) {
        
        NSLog (@"Successfully received the MyBeatDidDisconnectPeripheral notification!");
        NSDictionary *userInfo = notification.userInfo;
        CBPeripheral *myPeripheral = [userInfo objectForKey:@"peripheral"];
        NSLog(@"peripheral id: %@", [myPeripheral UUID]);
        
    } else if ([[notification name] isEqualToString:@"MyBeatDidUpdateState"]) {
        
        NSLog (@"Successfully received the MyBeatDidUpdateState notification!");
        NSDictionary *userInfo = notification.userInfo;
        CBCentralManagerState state = (CBCentralManagerState)[userInfo objectForKey:@"state"];
        switch (state) {
            case CBCentralManagerStatePoweredOff:
                NSLog(@"CBCentralManagerStatePoweredOff");
                break;
            case CBCentralManagerStatePoweredOn:
                NSLog(@"CBCentralManagerStatePoweredOn");
                break;
            case CBCentralManagerStateResetting:
                NSLog(@"CBCentralManagerStateResetting");
                break;
            case CBCentralManagerStateUnauthorized:
                NSLog(@"CBCentralManagerStateUnauthorized");
                break;
            case CBCentralManagerStateUnknown:
                NSLog(@"CBCentralManagerStateUnknown");
                break;
            case CBCentralManagerStateUnsupported:
                NSLog(@"CBCentralManagerStateUnsupported");
                break;
        }
    }
}
```