RCUE: Added Single-select Dropdown and Combo-box

Updated Gruntfile.js to create a non minified CSS file to easily debug.
Added example of single-select dropdown and combo-box in
dropdowns.html. Added jQuery for Combo-box to update input field with
selected menu item.
Added RCUE Breadcrumbs component
Clean up combo-box, single-select-dropdown, and variable less files

Removed unnecessary less nesting. Alpha sort variables.
Correcting order of variable