Tag Management UI Markup

References #3926

Static markup for the Tag Management screen

A few notes:
* Clicking the tag title now opens a settings menu on the right hand side, much like the new post settings menu
* The settings menu is also used when adding a new tag, only the delete button isn't there and 'Edit Tag' says 'New Tag'
* Search will not be included in the first implementation of this
* As with the post settings menu, clicking outside of the menu closes it
* The markup is dependent on child tags being nested _inside_ its parent. This makes them infinitely scalable.

```html
<div class="tag">
    ...
    <div class="tag">
        ...
    </div>
</div>
```