Fixed most build warnings

SOPE/NGCards/iCalAlarm.m

@@ -26,6 +26,7 @@
 
 #import "iCalAttachment.h"
 #import "iCalEvent.h"
+#import "iCalPerson.h"
 #import "iCalRecurrenceRule.h"
 #import "iCalTrigger.h"
 #import "iCalToDo.h"

SOPE/NGCards/iCalObject.m

@@ -20,6 +20,7 @@
 */
 
 #import <Foundation/NSString.h>
+#import <Foundation/NSTimeZone.h>
 
 #import "iCalObject.h"
 

SOPE/NGCards/iCalTrigger.m

@@ -19,6 +19,7 @@
   02111-1307, USA.
 */
 
+#import <Foundation/NSCalendarDate.h>
 #import <Foundation/NSString.h>
 
 #import "iCalEvent.h"

SOPE/NGCards/iCalXMLRenderer.m

@@ -33,6 +33,7 @@
 
 #import "CardElement.h"
 #import "CardGroup.h"
+#import "iCalCalendar.h"
 #import "iCalDateTime.h"
 #import "iCalPerson.h"
 #import "iCalRecurrenceRule.h"