Improve cross referencing between geni-cm and emulab datbases.
Add a datetime form to the shownodehistory we page so that a testbed admin can plug in a specific date, and find out what that node was doing at the time. Changes in the backend (node_history script) to support this. Note that the table is hard to seach for such a case, and so need to let node_history do its thing and then port process the records list. Unfortunately, the timestamps are unsigned ints, but perl does not handle those properly, so had to pull in Math::BigInt to deal with it. On the output page, include a link to the genihistory page if a node was part of a slice. On the genihistory page, add a new argument, slice_uuid, to look for the records for a specific slice.