Implemented recurrence for Day, Week, Month, Year.
Implemented postponing.
Improved recurrence. Different behaviour before dueDate, after dueDate, postponing
changes in settings
Implemented animation in add/remove reminder operation.
Shifted methods from ReminderItem to ReminderItemList as a result.
Fixed bug: Cell cannot retract.
Implemented recurrence setting in EditVC.
Fixed bug. Date changed in EditVC even when dateField is not selected.
Fixed bug. Prevent setting dates that have already passed.
Reorganised code in each file to be neater.
Remove redundant commented codes.
Stops NSTimer from running when ReminderList is not showing (appearing).