This commit does these things:
	- Adds Projects and ProjectsTest for basic operations with Project.
	- Ensures that delete operations preserves the database integrity (i.e.
	  no FK constraint exceptions). We do this in several ways:
		- By adding CascadeType.REMOVE in @OneToMany where appropriate (e.g: Projects->ProjectAssignment)
		- By manually setting to NULL orphan entities (e.g: Department->Employee)
		- By manually removing orphan entities when no @OneToMany is available
		  (e.g: Employee->ProjectAssignment)
	- Adds CascadeType.PERSIST in Project->ProjectAssignment to automatically persist ProjectAssignments
	  that were added to a given Project.
	- Refactors tests to avoid repetitive JDBC code that inserts some registers before the test.