Use java.time objects for the projects

[DavidWhitlock]

The Date and SimpleDateFormat classes are old and there is a lot of deprecated functionality. In Project 3, students are finding that the date parsing isn't strict enough, which is leading to a lot of confusion. I should explore replacing Date in the abstract application classes with something form the java.time package.

[abluescarab]

Hi David, I've messed around a bit with ZonedDateTime over in my repository. I initially used LocalDateTime but found that it defaulted to a timezone that did not print correctly, so I changed to ZonedDateTime.