Implement Lobby Functionality

[vkoves]

This is a task for both the back-end and front-end, but we should have lobby functionality so that games are a bit more permanent. Using some similar logic from Jackbox Party Pack, this might mean:

1. Lobbies have to be started, and generate a unique URL/code that can be used for people to join the lobby.
2. The lobby creator is the only one able to start the game, so that they can ensure everyone they want to be in the game has had a chance to enter.
3. If someone tries to join the lobby after the game has started, it tells them the game has started and either denies their request altogether or lets them spectate the game.

If we want to make this really nice, we should allow lobbies to be marked public or private. Public lobbies could be listed under a find lobby view (like with most multiplayer games), letting people join lobbies that haven't started games, or spectate games in progress. This issue is to hopefully kick off discussion regarding how we might want to move forward on lobby functionality.

[nathanshelly]

Some portions of this issue addressed in #12

We now support multiple lobbies which generate a code for other players to join the lobby. We do not currently let only the lobby creator begin the game. We also do not currently let people enter an in-progress game.