Standardised dropdown list item styles, Extracted page editor toolbar

Standardised dropdown list item styles, Extracted page editor toolbar

- Updated all dropdown list item actions into three specific styles:
  icon-item, text-item & label-item. Allows a stronger structure while
  prevents mixing of styles as we were getting for header dropdown in
  dark mode.
- Extracted out page editor top toolbar to its own view file & split
  editor switch options to different markdown options.