date: add two methods in Date class

Added isFirstDate() and isLastDate methonds in Date module

Signed-off-by: Zhengwang Ruan <ruan.zhengwang@gmail.com>
test: add tests for date

Added tests for both isFirstDate() and isLastDate().

Signed-off-by: Zhengwang Ruan <ruan.zhengwang@gmail.com>