Rationalise colour var names

[davidsauntson]

Currently the colour variable names are a bit all over the place and the design system colour palette includes product specific colours for advisernet. We need to:

• use a consistent approach to naming colour language variables so they can be more easily understood and overridden by products (suggest smth along the lines of ${component}__{element}__{property}--{state})
  • eg $cads-header__link-hover-colour should be smth like $cads-header__link__color--hover
• remove advisernet product colours from palette and add into product specific css