Add signals for interaction with controls

I propose the following signals:

• toggled for AbstractButton
• sliderMoved to Slider
• dialMoved to Dial
• textEdited to TextField (or even TextInput directly)

All of these signals should be implemented like in widgets and only be emitted when a user interaction happened. See e.g. QLineEdit::textEdited.

SpinBox should have a similar signal, but QAbstractSpinBox is missing one.
I propose valueEdited.

This makes it easier to update a property in the backend if and only if the user changes a control.
This avoids subtle bugs when e.g. a control rounds the value of the backend and pushes back the rounded value to the backend, because the front end code does not distinguish between a change of the value and an interactive change from the user.