Add statistic collection command

[Dave Shoreman]

We need certain information about the sytem to be collected continously over time so that we can use that data for graphs etc..

The best way to do this (without using another language, which is the long-term plan) would probably be to throw it into an Artisan Command. This would run every minute or so, running the various stat commands in the shell and saving the important bits into a db table.

With stats being saved into the database we'd also need a way to get them back out again. A basic Eloquent model will probably be plenty for the dashboard stats, but an extra API endpoint might be needed to get the historic data for graphs.