Merge branch 'quality_control'
Integrate JournalController to Logic to support undo/redo.

There is no working version of Delete action so was not added.
Add command distribution to undo/redo in Logic.executeCommand

Now undo/redo should work
Merge branch 'journal'
Added hasStartDate, hasEndDate to DatePair

Added hasStartDate and hasEndDate methods, refactored and remove unused
import by all classes
Added method to check if Task's dateList is empty
Merge branch 'master' of https://github.com/cs2103aug2014-w11-4j/main

Fix Conflict