Add menu to index.html
Remove old frame styles

Delete old, obsolete frame-related sass files and styles and replace
them with a new file for menu styles.
Add some variables for font size and weight as well as light grey

Add variables for three different font sizes as well as a variable for
the semi-bold font-weight, and a new light grey color. Set font-size
and font-weight of top-menu and set default font size to 16px.

Finish top menu and add dropdown carets and filter-menu positioning
Change header menu structure

Update styles to reflect the change to the menu structure:
header containing two menus.