Support for both LDAP and LDAP3 clients

[jimlambrt]

Is your feature request related to a problem? Please describe. Currently, we only support binding with an LDAP3 client and clients using the previous version of the protocol are unable to bind.

Describe the solution you'd like Support both LDAP and LDAP3 clients but allow the developer an option to only support LDAP3 if they wish via a new Option when creating a NewServer. This new WithRequiredVersion option will have to be passed along from the Server to each new conn and then to each new request, so it can be enforced when the new message is created.