BugFix #0002622: The server Dovecot use by default an UTF-8 and by doing...

... so it cause a wrong re-encoding in UTF-7 when reaching the sieve server (knowing that the foldername in sieve are encoded in UTF-7). Since it is not the case with a Cyrus server, I created a new variable available in the sogo.conf that let you specified the type of encoding you need. By default the encoding is set to UTF-7. ex : SOGoFolderEncoding = 'UTF-7'