Migrate Entry over to using Joda Time

* Fix some whitespace issues
* Add .DS_Store to .gitignore

This pull request shouldn't be merged in until https://github.com/coldstar96/cse403/pull/45 is merged in, since that will definitely cause some merge issues on my end that I would need to rectify. However, please code review what I currently have so the process can be sped up a bit.