Correction LDAP validation (#342)

Correction LDAP validation (#342)

* Correction LDAP username validation

As https://msdn.microsoft.com/en-us/library/aa366101(v=vs.85).aspx describe spaces should not be in start or at the end of username but they can be inside the username. So please check my solution for it.

* Check for zero length passwords in LDAP module.

According to https://tools.ietf.org/search/rfc4513#section-5.1.2 LDAP client should always check before bind whether a password is an empty value. There are at least one LDAP implementation which does not return error if you try to bind with DN set and empty password - AD.

* Clearing the login/email spaces at the [start/end]