Add support for configurable time-outs

[Kabouik]

Would it make sense to allow customizing nmail strategies for synchronizing, fetching, reconnecting, staying idle, staying offline, how many retries and how long between them, when to check if Internet connection is working, etc., with configurable time-outs for each of these background actions?

[d99kris]

Yes. There are some configurable timeouts today (idle_timeout and network_timeout) but there may be some additional things we can make configurable. Right now nmail is optimized for minimizing network traffic, but I can look into adding some option to make it detect offline status and reconnect faster.