Fix the bug allowing to add duplicate requirement
Add error message to warn duplicate requirement
Add error message

An error message would appear when users use a name
of an existing requirement
Change condition to add requirement

Requirement must have different names to be added.
Before this commit, user can add requirements with the same name but different descriptions
Merge remote-tracking branch 'origin/dev-fixAddDuplicateReq' into dev

Conflicts:
	PlanningPoker/src/edu/wpi/cs/wpisuitetcw/modules/planningpoker/controllers/req/AddRequirementToSessionController.java
	PlanningPoker/src/edu/wpi/cs/wpisuitetcw/modules/planningpoker/view/overviews/viewSessionComp/ViewSessionReqPanel.java