Remove unused use statements, fix comments
Fix 'Call to a member function saveMessage() on array' error when sending an email

Log entry:
/index.php/apps/mail/accounts/1/send - Call to a member function saveMessage() on array in <webroot>/owncloud/apps/mail/lib/controller/accountscontroller.php on line 265
Merge pull request #405 from wurstchristoph/master

Remove unused use statements, fix comments