Keep a short term log of item movements

[shantek]

When a player leaves you items in your post box, ideally we should log these transactions. If a player received mail while they were offline, this would then show a log of who left the mail and what they left them.

They could see the log with a command like "/postoffice log"

Investigate the best way to store this, how long we'd want to keep records for, if we manually delete the log with something like "/postoffice clearlog" or if it simply is cleared when they open their post box.

Also investigate the best way to store all this data. Do we move everything to a flat file db?