* The "Story Mode" button on the MainScene opens the levelpacks window.
* Levelpacks from all places are shown (built-in and user files), basic
level picker works.
* When playing a level out of a levelpack: the PlayScene gets the file
data from the zipfile and plays it OK.
* When a levelpack level is solved, the "Next Level" button appears on
the success modal and hitting Return will advance to the next level in
the pack. The final level doesn't show this button.
* The user can edit levelpack levels! Clicking the "Edit" button on the
Play Mode moves the loaded level over to the EditScene and the user
could save it to disk or edit/playtest it perfectly OK! The link to
the levelpack is lost upon opening in the editor, so the "Next Level"
victory button doesn't appear.
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.
