[LdapSource] applied visibility keywords
[LdapSource] fix coding standards
[LdapSource] replaced deprecated functions
[LdapSource] fix readability of enumeration
[LdapSource] fixed arguments and indentation of calculate methods
[LdapSource] logs query error
[LdapSource] fixing coding standards
[LdapSource] replaced unknown fatal_error() with throwing Exception
[LdapSource] replaced hardcoded ldap_* functions with wrapper function.
This change is almost for testing.
[LdapSource] added minimum test case
[LdapSource] fixed errors around connect()