Merge branch 'develop'
Add method update() which is to be called after registerObserver()
Define NOP notifyObservers()

NOP -> No Operation
Remove update() declaration, now inherited from Model
Add NOP update() definition
Create abstract models for SubTaskPanes
Define updateTitle() from PaneModelObserver
Define root observer type for SubTaskPane
Create Observer for CreateItemPane
Create Model for CreateItemPane
Make implement CreateItemPaneModelObserver
Create @Bean for CreateItemPaneModel
@Inject CreateItemPaneModel
Call update() in registerObserver
Remove registerObserver() as it is redundant
Remove println statement added to test app
Merge branch 'iss35-create-title-for-subtaskpane' into develop