Added specific quota script for Dovecot 2.x.x
Fixed #908: Review - Dovecot - Quota - Switch to maildir quota backend
Fixed #909: Enhancement - Courier - Quotas support using maildrop MDA
Fixed #917: Defect - Unable to switch from Dovecot to Courier
Fixed: Dovecot sieve plugin parameters should not be part of i-MSCP configuration files.
Fixed: Dovecot quota warning service not working
Fixed: Dovecot warning script placeholder
Updated Dovecot configuration files (Removed useless parameters + small fixes)