Legend wizard for both layer and style

This PR introduces two wizards that have been asked in #389, #388, #387 and maybe in other places. I've designed it so that successive panels are managed by a SIFWizard. In order to make things simpler, I've added a method in UIFactory to build a SIFWizard and another one to display it and return its exit boolean. This offers me the ability to introduce listeners to customize the buttons' behaviour.

The WizardPanel is mainly a ILegendPanel. It hosts a text field too, where the user has to configure the name of the symbolizer or style, depending on the situation. WizardPanel is a LegendContext and can consequently be associated to ILegendPanel instances.

The behaviour is the following:
- If launched from a right click on a layer, the generated symbolizer is put in a dedicated style and this style is added in the layer.
- If launched from a right click on a style, the generated symbolizer is put in a dedicated rule that is added in the style.