Unit Tests For DateUtil

Hi Guys,

Thanks for sharing your codes. I added some unit tests to the `org.broadleafcommerce.common.util.DateUtil` class, and notice that the `DateUtil.isActive()` method returns true even when `endDate.getTime() == now`. I would expect it to be otherwise (an offer should be inactive when the end datetime is now, right?) **UPDATE: I guess it really doesn't matter since the representation is to the milliseconds**

Feel free to merge the unit tests to the project if you think they will be helpful. I will send more pull requests if I come out with more useful unit tests.