Turning public 4 Liquid helpers (NSDate and UIColor)

+ (UIColor *)colorFromString:(NSString *)hexString;
+ (NSString *)hexStringFromUIColor:(UIColor *)color;
+ (NSDateFormatter *)isoDateFormatter;
+ (NSDate *)gettDateFromISO8601String:(NSString *)iso8601String;

Signed-off-by: Miguel M. Almeida <miguelcma@CMA-Retina.local>