* SDL2 builds of the game now set their app window icon.
* Create/Edit Level window is updated to show a tabbed UI to create a
new Level or a new Doodad. The dedicated main menu button to create a
new doodad (which immediately prompted for its size) is replaced by
this new tab's UI.
* Edit Drawing/Play Level window is more responsive to smaller screen
sizes by drawing fewer columns of filenames.
* Bugfix: the Alert and Confirm modals always re-center themselves on
screen, especially to adapt between Portrait or Landscape mode on a
mobile device.
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.