Add ingraph-housekeeping-daemon
check_ingraph: Fix xmlrpclib.Fault: <Fault 1: "<type 'exceptions.AttributeError'>:'NoneType' object has no attribute 'interval'">

Remove hardcoded interval from getPlotValues2 calls since the interval may not exist.
Further the daemon automatically determines the best fitting interval when unset.
check_ingraph: Fix TypeError: unsupported operand type(s) for +: 'float' and 'NoneType'

Exit gracefully when there's no data for either the first or the second interval.
Fix default values for warning and critical in check_ingraph

It makes more sense to have warning=10 and critical=20, instead of vice versa.