Admin list filter

Admin list filter populates your right sidebar with options to filter your objects. Like in Django
An example of how it could be used.

listFilter := &core.ListFilter{    URLFilteringParam: "IsSuperUser__exact",    Title:             "Is super user ?",}listFilter.OptionsToShow = append(listFilter.OptionsToShow, &core.FieldChoice{DisplayAs: "Yes", Value: true})listFilter.OptionsToShow = append(listFilter.OptionsToShow, &core.FieldChoice{DisplayAs: "No", Value: false})

Later on we will migrate it to interface as well, so it could be used easily for any type of list filter functionality.