Make IMAP option "Create new threads"  work

there is already this option but id doesnt works : "Create new threads" (Create new threads for unrecognized emails )

When you check that option the PS_SAV_IMAP_CREATE_THREADS variable is correctly set, and indeed messages are really scanned and imported and customer threads created in database for "unrecognized mails" but they never show on BO because the shop_id is 0 for those ct and some other bug inside the controller

this modification allow that option to work, simply showing in backend imported messages 

plus I added 2 new functionalities:

1) th controller it is now able to insert the message in the right customer thread "category" (if you have more than one like support or suggestions etc..) depending on the mail the message is directed to.

2) the controller it is now able to detect if the mail sending the message is owned by one of the registered customer and assign it to him showing customer details correctly (like customer name)