MT#5879 Make email invoices query simplier.

Remove redundant link through contract_balances to contracts.
Process customer email template and add month and year into invoice data.

share/tools/generate_invoices.pl

@@ -131,6 +131,7 @@ sub process_invoices{
                     ),  { Slice => {} }, @{$opt->{client_contract_id}}, v2a($client_contract->{id}), v2a($stime->ymd),v2a($etime->ymd) );
                 }
                 if($opt->{send} || $opt->{sendonly}){
+                    my $email_template = get_email_template($provider_contract,$client_contract);
                     my $email_template = get_email_template($provider_contract,$client_contract);
                     email($email_template, $provider_contact, $client_contact, $invoices->{$client_contract->{id}} );
                 }