amend playgun prefab
merge
Add gun tutorial for player, so the player can pickup gun, and shoot enemy, but still has some weird problem:
1.In level0.1, the PlayerGun prefab does not collider with Player, but will collider in any other levels
2.In level0.2, the PlayerGun does not flash when putting Player in the scene. But will flash in any other levels.
3. In level0.2, when Player pick up the gun, the children 'gun' of the Player prefab will disappear for no reason...