Introduce scss

    Refactor the CSS to use SASS/SCSS
    
    I have moved the original CSS file to solidare-it.scss, then did some
    refactorings to leverage some of the benefits of SCSS. In particular
    I seperated the color palette definition from its use.
    
    Note that even though I have included the CSS file that is now generated by
    SASS, it should never be directly edited!
    
    To install SASS, given you have Rubygems available is simply
    
      gem install sass
    
    To then generate the CSS from the source file, use
    
      sass solidare-it.scss:solidare-it.css