move view filter into table, add combined filter widget, fixes #3421

app/controllers/admin/courses.php

app/views/admin/courses/sidebar.php

lib/classes/ActionMenu.php

lib/classes/sidebar/SelectListElement.php

resources/assets/javascripts/lib/admin-courses.js

resources/assets/stylesheets/scss/admin-courses.scss

resources/vue/components/AdminCourses.vue

resources/vue/components/StudipActionMenu.vue

templates/shared/action-menu.php