Add more controls to the menu bar

Chunky should make more use of the menu bar.

Controls that exist in the context menus of the `Map` tab and `Render preview` tab should also exist in the menu bar under a `Map` dropdown menu and a `Render preview` dropdown menu, respectively. This is to provide an alternative location for the controls, so that new users who do not know that the map and render preview can be right-clicked can still find and access the controls. Additionally, at large canvas resolutions, the render preview becomes invisible, rendering controls located in its context menu inaccessible.