Adds standard deviation to the GUI.
Adds setter for the standard deviation text field.
Added functions/tests for calculating variance and standardDeviation.
Enable displaying the standard deviation of a requirement.
Merge remote-tracking branch 'origin/dev-StandardDeviation' into dev

Conflicts:
	PlanningPoker/src/edu/wpi/cs/wpisuitetcw/modules/planningpoker/view/CompletedSessionEstimatePanel.java