Changes in ProfileManagerWidget

Set a QAbstractItemModel * variable when constructing the object, store
both the original model of profile table and the proxy model
Modify signature of methods

Add default model index in rowCount() and columnCount()
Create data mapper in ProfileManagerWidget
Add button to apply changes in profile manager
Refactor in ProfileManagerWidget

Changed name of private slot
Set icon to apply changes button

In ProfileManagerWidget
Implement apply changes functionality

Still to be checked the submit policy and mechanism of QDataWidgetMapper
Changes in ProfileManagerWidget
Fix bug in ProfileManagerWidget

Fix bug that prevent submit() method of the mapper to work after the
first time. Bug happened because after the first submit the index of the
mapper was reset to -1, preventing following submits
Add placeholder text where necessary

In ProfileManagerWidget
Check dates in ProfileManagerWidget

Display a KMessageWidget when dates are incorrect
Create a slot to handle context menu request
Add context menu to ProfileManagerWidget

Add a context menu with two actions:
- View picture (at a larger size)
- Change picture
Slots have not been implemented yet
Change icon of action in context menu
Implement view picture slot in profile manager
Move the picture label to the center of the screen
Install event filter on picture label

Make the widget close when escape key is pressed
Change flags of picture label
Modify modality of picture label

Set to Qt::ApplicationModal
Move profile picture size const

Move ProfilePictureSize constant from VRDatabase to file constants.h