Add ability to inject custom calendar with backward compatibility

JTCalendar/JTCalendarManager.h

@@ -34,6 +34,7 @@
 @property (nonatomic, readonly) JTCalendarScrollManager * _Nullable scrollManager;
 
 - (instancetype _Nullable )initWithLocale:(NSLocale *_Nullable)locale andTimeZone:(NSTimeZone *_Nullable)timeZone;
+- (instancetype _Nullable )initWithCalendar:(NSCalendar *_Nonnull)calendar;
 
 - (NSDate *_Nonnull)date;
 - (void)setDate:(NSDate *_Nullable)date;

JTCalendar/JTCalendarManager.m

@@ -27,9 +27,24 @@ - (instancetype)initWithLocale:(NSLocale *)locale andTimeZone:(NSTimeZone *)time
     return self;
 }
 
+- (instancetype)initWithCalendar:(NSCalendar*)calendar
+{
+    self = [super init];
+    if(!self){
+        return nil;
+    }
+
+    _dateHelper = [[JTDateHelper alloc] initWithCalendar:calendar];
+    [self commonInit:calendar.locale andTimeZone:calendar.timeZone];
+
+    return self;
+}
+
 - (void)commonInit:(NSLocale *)locale andTimeZone:(NSTimeZone *)timeZone
 {
-    _dateHelper = [[JTDateHelper alloc] initWithLocale:locale andTimeZone:timeZone];
+    if (_dateHelper == nil){
+        _dateHelper = [[JTDateHelper alloc] initWithLocale:locale andTimeZone:timeZone];
+    }
     _settings = [JTCalendarSettings new];
 
     _delegateManager = [JTCalendarDelegateManager new];

JTCalendar/JTDateHelper.h

@@ -10,6 +10,7 @@
 @interface JTDateHelper : NSObject
 
 - initWithLocale:(NSLocale *)locale andTimeZone:(NSTimeZone *)timeZone;
+- initWithCalendar:(NSCalendar *)calendar;
 
 - (NSCalendar *)calendar;
 - (NSDateFormatter *)createDateFormatter;

JTCalendar/JTDateHelper.m

@@ -27,6 +27,17 @@ - (instancetype)initWithLocale:(NSLocale *)locale andTimeZone:(NSTimeZone *)time
     return self;
 }
 
+- (instancetype)initWithCalendar:(NSCalendar *)calendar
+{
+    self = [super init];
+    if (self) {
+        _calendar = calendar;
+        _locale = calendar.locale;
+        _timeZone = calendar.timeZone;
+    }
+    return self;
+}
+
 - (NSCalendar *)calendar
 {
     if(!_calendar){