Adds ShuffleDeck class for deck behavior.

We'll want to draw things like songs and country flags from a deck
to avoid random-induced repetition.
Adds SVG used for timer sprite mockup.
Adds flags for countries of the world.

Flags are loaded in `LevelManager#OnEnable`, where names are sanitized
and the collection of textures is converted to a ShuffleDeck for
assignment to timers.
Adds a quit key because GAME JAM GAM
Adds FlagManager.

FlagManager tracks flag sprites and country names for a timer.

Fixes a bug that was causing too few rows to be drawn.