#1 sample span aggregation

[Enrico Zanolin]

KNOWN ISSUE

One issue that you should be aware of is that totals
are grouped by sample date which means they will always
be 5 mins out. eg A sample taken at 07h00 actually
spans from 06h55 to 07h00 but it belongs to the 07h00
hour aggregation.

Fixing it requires adding an additional lastsampled
date to the port table and a lastsampled field to the
collector along with some minor additions to the
collector.php script.

I do not require the accuracy so I havent bothered with
it, I dont mind that hour 7 is actually from 6:55 to
7:55, others may not find this to be acceptable