Added some defensive coding

Also added unit test for functions in displayView and FilterTasks
resolve conflict
Resolve conflict
Merge remote-tracking branch 'origin/master'

Conflicts:
	src/chirptask/common/Settings.java
	src/chirptask/logic/DateParser.java
	src/chirptask/logic/Logic.java
	src/chirptask/testing/JUnitLogic.java