Allow user to choose a character before playing

[isuru89]

When user is first time logged-in, allow user to choose his/her favourite character for playing game.

There are predefined set of characters which user can select which is defined by admin at the deployment time.

User cannot change his/her character once chosen, but the admin can modify by the request of the user again only once in a lifetime. In such change, user will lose all his/her character purchases.

Such change of character should not affect to leaderboards, points, badges or any other game scoring mechanics.