JBIDE-18670 HTML5 Palette: Palette model refactoring

new palette model implemented
Wizard instance is created too early. It should not be cached, and should be created by requesting paletteItem only in createDropWizard().
Implementation of getCustomWizardName() is not needed - it is used here only to check if wizard is available. Hence IPaletteItem just needs method hasWizard().
Old implementations called getCustomWizardName() to create wizard. Here, as wizard is created by IPaletteItem it should also answer if it can be created without actually creating it.