Daemon mode

[gmp216]

Implement daemon mode (-d) with "fetch-frequency" configuration option (default 5 minutes). Fork into the background with daemon() and log to syslog, looping through accounts fetching all folders. On errors, try to restart.

To do: --complete signal handling --replace sleep() calls with I/O polling

[stspdotname]

I would love something like this. If it prompts for passwords at startup, it would make saving passwords in the config file unnecessary.