Feature request: checkout shutdown on timeout

[kaizushi]

I use the monerowp code for a few customers on my system. I am in an unusual position regarding the connection the code makes to third party sources. This connection can become undone on my system, which uses a SOCKS proxy to reach a server which gives it Internet connectivity. Basically everything goes thorough a transproxy (redsocks) and to this remote server. This complicated setup sometimes goes down for a while, and monerowp runs but on outdated prices.

The code for this extension would be much improved if it kept note in the database of when it was last able to conect. Then you could have an option one sets on how long without a connection it takes until the checkout goes offline automatically. The current code when it loses the connection keeps running, but with outdates Monero prices.

Looking at the code one would just need to add a config option to set how long the system goes without Internet before going down. It could just check the timestamp in the table for Monero prices. One should also be able to choose a message to display when the Monero checkout goes down from the timeout.