Added an error message bag for connection issues with LDAP

[Godmartinz]

This adds error handling around LDAP login. if it times out, it does so with an amorphous response:

[Godmartinz]

@uberbrady I made some changes around the self::bindAdminToLdap($connection), You left a warning about it. but I think with the throws, it should be handled now. But I really would like your blessing or input on this before this moves forward.
The tests were failing because the if statement on Model/Ldap.php:173 was returns on failure and nothing on success, I am just calling self::bindAdminToLdap($connection) instead now. Let me know iwhat you think. Please and thank you 🙂

[Godmartinz]

@uberbrady gentle poke, do you have any thoughts or issues with this?

[uberbrady]

I think I would be okay with this if it, say, showed an error (only to a superuser) about how it needed to fail through LDAP to do local login, I think something like that would be just fine - and useful. But showing ldap errors or codes to unauthenticated users could disclose to an attacker that LDAP was being employed - and might even disclose the IP address in an error message - something like "Could not connect to 1.2.3.4 port 636" - that could be very dangerous.

Also, the LDAP system has been pretty heavily re-worked recently, so this PR is pretty heavily conflicted. If you want to try and get it back into a mergable state, I will definitely take another look at it, but I'm still generally pretty nervous about this approach for security reasons.