fix missing import in model_test
add a get-player function
rename create-user to create-player
make create-player return the id of the new player
update README after refactoring/renames

create-game is no longer needed here since that's now possible through
the UI
add a `players.looking` column

this should show when a player is looking or available to start a new
game
create a game_invitations table

to be used for inviting other players to games
move database initialization to a leiningen plugin