Add Task retrieval, updating, and deletion to database

For information about how to call methods in the TaskEntityManager, see this wiki page:

https://github.com/WPI-Suite/wpi-suite/wiki/Networking-with-janeway#http-requests-and-addressing-in-wpi-suite
Update TaskEntityManager.java
Merge pull request #15 from R2-Team2/feature-41-server_task_creation

Add Task retrieval, updating, and deletion to database