Add styles to settings dropdown-menu

- added new styles to the dropdown menu
- added icons to menu items
Merge branch 'dev-angular' into feature/toolbar-dropdown-menu-styling

Conflicts:
	app/assets/stylesheets/fonts/_openproject_icon_font.sass
	app/views/work_packages/index.html.erb
Merge pull request #1295 from opf/feature/toolbar-dropdown-menu-styling

Feature/toolbar dropdown menu styling