Add "Library" menu

[iznaut]

microgames should be playable individually, for practicing and for high score chasing. each microgame submission would be expected to include a title (and description?) that would be displayed here, along with usernames for the contributor(s). it would also be ideal to have a screenshot of the microgame, though that might be a bigger discussion (do contributors include their own or do we capture that automatically?)

eventually this menu should have extensive filtering and sorting options (genre, difficulty, most liked by community, games by creator, etc) but we'll worry about that when we have more games!