Layout: Add more customization options

[ackzell]

Changing the visibility of the preview pane (Output.vue in the repo) is useful and currently not supported by the official @vue/repl package. There are other things we want to control dynamically from YV:

Preview Pane

• Show / hide the preview pane

Console

The console (from #15) will live inside the preview pane in a first implementation. We want toggles for:

• Show / hide the console
• Side by side, top & bottom

Reverse layout

Editor first -> preview second or viceversa

Intentionally not adding reverse layout for the preview/console, but we'll see if that is a requested feature later on.

[ackzell]

Closed in #33