Enable account level changing at runtime

[yungcomputerchair]

Modifies the /access command to allow changing of account level at runtime (fixes #194).

Usage: /access <id> [new_level]
Use . for id to select yourself

The player can only modify the account level of someone with weaker privileges, and can only assign privileges weaker than their own. This change is persistent (immediately written to the database).
If no new level is provided, the command just prints the current access level of the player.

Using this command on other players is only permitted at access level 30.

[CakeLancelot]

Thanks!