major design changes (dark mode)

app/Http/Controllers/StartpageController.php

resources/less/metager/general/base.less

resources/less/metager/pages/resultpage/result-page.less

resources/less/metager/parts/searchbar.less

resources/less/metager/parts/sidebar.less

resources/less/metager/startpage-only.less

resources/less/metager/variables-dark.less

resources/less/metager/variables.less

resources/views/index.blade.php

resources/views/layouts/resultPage.blade.php

resources/views/layouts/resultpage/resources.blade.php

resources/views/layouts/staticPages.blade.php

webpack.mix.js