Rename Options to HandlerOptions

Options is too generic for this type usage
Add support for replacements in RedirectHandler
Set the flag names explicitely in the dev options
Rename gnd.la/admin to gnd.la/commands

Admin will be used for an administrative type application, which
will allow editing models as well as running registered commands.
Don't default to notnull and omitempty for bool fields

That would send a NULL to the db when the field is false, which
might not be desirable.