Fix LDAPc for using empty firstName and emptyLastName in User

 - when lastName is null, use 'N/A' instead
 - add this fix to Main.java
 - add this fix to createUser in LDAPc
 - add this fix to updateUser in LDAPc
Merge pull request #591 from stavamichal/fixLdapcForEmptyLastName

Fix LDAPc for using empty firstName and emptyLastName in User