The title screen is now responsive to landscape mode. If the window is
not tall enough to show all the menu buttons (~600px) it will switch to
a horizontal layout with the title on the left and buttons on the right.
WIP "Story Mode" button that brings up a Level Packs selection window.
Adds `doodad levelpack create` and `doodad levelpack show` commands to
the CLI tool to create levelpacks.
A levelpack is a ZIP file containing a descriptive index.json and
directories for levels and doodads.
