Changed register_self to register_flags

This means:

0 ... disable !register command (will not be shown in !help either)
1 ... enable self-registration
2 ... notify ops (send application for registration)

Default value 1.

Example:

1)
We want to let users register themselves and notify ops about the result.
register_flags=3

2)
We want to enable !register command, but only ops can register new users. So guests must send application.
register_flags=2