Add basic account creation stubs

This patch adds a new set of modules under game/accounts to manage account
creation, along with a new set of commands to handle account creation. A fair
amount of this is just stubs, but it provides some basic structure for what
should follow.

This includes the following:
- Add init_accounts to create the account in the data backend
- Add module 'createaccount_command' for account creation
- Add module 'password_command' for entering a password for an account
- Add module 'username_command' for entering an account username
- Add account retrieval, creation function in accounts module