Enhancement: change from hardcoded colors to LESS each

[mikejf-pr]

As of less 3.7, less supports looping through a dynamic map of variables to create a set of objects. Example:

@set: {
  blue: #00f;
  green: #0f0;
  red: #f00;
}
.set {
  each(@set, {
    @button-@{key} {
         background-color: @{value};
     }
  });
}

Using this kind of mapping, it should be possible to change SemanticUI to generate colored variations for whatever pallete we want dynamically.