Resolves#1313
What this commit does:
* Whenever the Apply button is pressed, and if the save was successful, then the Apply button is disabled.
* Each subwidget used by EditEntryWidget has now a signal called `widgetUpdated` that is emitted when the widgets' internal content changes. The EditEntryWidget subscribes to that signal to know when to enable the Apply button (by calling `entryUpdated()`).
* There are some views that are not isolated in their own widgets (`m_advancedUi`, for example) so in those cases I invoked `entryUpdated()` directly whenever I detected an update:
* some updates occur directly in a Qt widget like when editing the text of a QLineItem, so in that case I connected the widget's signals directly to the `entryUpdated()` slot.
* some updates occur in EditEntryWidget, so in those cases the invocation to `entryUpdated()` is made as soon as the change is detected (for example when the user has confirmed an action in a dialog).
A known problem: there are some situations when the Apply button will get enabled even if there are no changes, this is because the app changes the value of a field by itself so it's considered an update (for example, clicking on the "Reveal" button changes the text shown in a text field).
The solution to this can be a bit complicated: disabling temporarily the `entryUpdated()` whenever the app is going to do an action with such side-effects.
So I preferred to let the Apply button get enabled in those cases.
Chnage to one method to set MessageWidget text passing type as
parameter.
Only messages with questions requiring user input reamin using
MessageBox dialog.
Use signal/slots to set message in MessageWidget and hide message,
signal/slots only used when required.Maybe need to change all calls to
signals/slots in the future.
