(CFACT-48) Add structured uptime fact

This commit adds a new 'system_uptime' fact, which returns a map including
keys for seconds, hours, days and a human readable uptime.

Also, the existing uptime facts were updated to take their values from this new 
structured fact, rather than resolving them individually.
Looks like the spacing here is still at 2.  Should be the last thing that needs to be fixed before merge.