Turn on the first real use of Qt, replacing the creation_time in our waypoints

Turn on the first real use of Qt, replacing the creation_time in our waypoints
with a QDateTime which will (eventually) give us coherent times before 1970
and with decent sub-secont support.   This patch itself doesn't really give
us that, but it lays important steps.

Right now, it's conditionally compiled under NEWTIME, but I don't expect that
to last very long.  We'll move to *requiring* Qt very quickly; this is a prop
for ease of development right now.