Combined LDAP connect and bind for failover handling

Not totally happy with the complexity in approach, could maybe do with
refactoring some of this out, but getting a little tired spending time
on this.

app/Exceptions/LdapFailedBindException.php

@@ -0,0 +1,7 @@
+<?php
+
+namespace BookStack\Exceptions;
+
+class LdapFailedBindException extends LdapException
+{
+}