Task#5059 - Workarround for performance and load improve

    Created pingquietinterval parameter with default 170 sec. It defines how much the ping don't access database and IMAP to save resources.

   Created nosyncinterval parameter with default 300 sec. Within this interval, data is not synchronized with database and IMAP. Each time it expires, a normal synchronization is done.

   Implemented perfomance improvement in folderSync command.

   Corrected how old ping commands are killed.