[FIX] ModuleADSS - Make new site link page works

[mmarsac]

Make new site link page works

Using an LDAP search, retrieve all available sites in order to build a new site link.
A minimum of two sites is required to create a site link. If fewer than two sites are found, an error message is displayed instead of the standard constructor page.
If exactly two sites are available, they are automatically added to the new site link. Otherwise, the user can select the desired sites from a list of all available sites.

By default, the cost value is set to 100, and the replication interval is set to 180.

[osvegn]

A good practice is to split your code in different kind of function / procedure:

• Logical: Takes arguments and does some modification / check.
• Integration: Call that requires an established connection.
• UI: Get / Set information to UI.
  It will help to provide tests.

For example (pseudocode):

/// Retrieve information from UI. -> UI tests
function GetDistinguishedName: RawUtf8;
begin
  result := Edit1.Text;
end;

/// Use LDAP protocol to retrieve data -> Integration tests
function RetrieveObjectClassAttribute(ADistinguishedName: RawUtf8): TLdapAttribute;
begin
  result := TLdapAttribute(LdapClient.SearchObject(ADistinguishedName, '', 'objectClass').clone);
end;

/// Only check data -> Unit tests
function IsObjectUser(AAttribute: TLdapAttribute): Boolean;
begin
  result := AAttribute.GetReadable(Pred(AAttribute.Count)) = 'user';
end;

/// Helper function that does all in one.
function IsSelectedObjectUser(): Boolean
begin
  result := IsObjectUser(RetrieveObjectClassAttribute(GetDistinguishedName));
end;