Applications category subcategories are directly accessible from the drawer and other visual changes

Changed some visual things based on the given design: https://www.figma.com/file/gjuIy1rxU9xHkaJXM0pasK/Ocean?node-id=715%3A3330

Drawer shows directly all subcategories from Applications category. Made the change in QML and didnt change the XML file. Install button shows now a icon and defaults to a icon only button on smaller screens. Changed ApplicationDelegate.qml to given order. Changed the page background to darker color so it differs more from drawer and header. Changed "Updates" action background color to themes green. Maybe there should be more vibrant color but this is todo for the theme devs. Sources icon better placement under the install button. Featured ApplicationDelegate now have more info than a regular card.