set user level rng and add game utils module

[zgeoff]

• new seed field attached to user. generate by using createSeed util
• migrations
• new lib-game-utils module
• move utils into there
  • rng
  • getSeed (rename to createSeed)
• new util:

// combine seed function
function combineSeeds(a: number, b: number): number {
  return ((a ^ b) * 0xDEADBEEF) >>> 0; // >>>0 ensures 32-bit unsigned
}