Removed @ operator from dol_include_once

Adding @ operator to include_once makes include errors untraceable, it shouldn't be there. Errors must be thrown so that we notice them. It is PHP configuration's choice to decide wether to log them or print them.
Avoiding include in case of unexisting file
Corrected file_exists check and little refactor
Added missing doActions for supplier order fiche.php
Refactored Dolibarr triggers:
Created a DolibarrTriggers abstract class.
Moved common variables out of construct class
Improved run_trigger method signature
Removed useless code
Fixed trigger not returning anything under some circumstances
Converted some global variables to local ones in InterfaceLogevents
Fixed little bug
Added missing $error and $errors variables
Refactored InterfaceNotification class
Corrected test
Refactor InterfaceActionsAuto
Corrected CS errors
Accidentally removed Demo trigger content
Fix: Translation
Fix: add curl_setopt($cHandler, CURLOPT_SSL_VERIFYHOST, false);
Fix: SQL syntax error with pgsql
Fix: For contract, only services available by default. Product appears
if option is set only.
- New: Enable feature developed for 3.6 we forgot to enabled: Adding
prefix on uploaded file names. 
- New: No more dependency between contract and service module.