Refactor user input fields

[Andreas]

Actual behaviour

All input fields are text fields.

Further, the custom ItemPicker control does not have a dedicated label.

Expected behaviour

By now, UIToolkit has dedicated fields for integers and floating point values. These could be used instead of the basic string text fields.

Further, every default control of UIToolkit has a dedicated label property. This label can easily be customized using style sheets. Similarly, the custom ItemPicker should get a label property.
This will simplify the UI hierarchy considerably because at the moment an extra container and label is added for most ItemPickers. Thus, instead of container+label+ItemPicker it would be reduced to only the ItemPicker, which includes a label and serves itself as container.