Add dropdown menu, advanced list content and message components

[tdanecker]

Add some more components from semantic-ui:

• Dropdown.Divider
• Dropdown.Item
• Dropdown.Menu
• List.Content
• List.Description
• List.Header
• List.Icon
• Message

The style how parentheses were used in the keys.clj file was very inconsistent. I changed them to a parinfer style in a separate commit so that it's easier to work with this file.

Also, I fixed a typo in the dropdown keys.

Just let me know if I should create separate PRs for those changes.

Also, I'm not that happy about dropdown-menus for now. It has to be called as a function instead of a component. Otherwise the dropdown-menu wouldn't open when clicked. I suspect that the Dropdown expects the Dropdown.Menu as a direct ancestor but sodium would introduce a small wrapper-component in between which messes things up.

[na/dropdown {}
  (na/dropdown-menu {}
    [na/dropdown-item {:text "menu item"}])]