Use the right event type

11 is SAMPLE_EVENT_GASCHANGE, and thats the one that doesn't contain any
He-part. The type where He and O2 is packed togeather is 25,
SAMPLE_EVENT_GASCHANGE2.

Left to implement is to figure out the type of the event when we read
the xml, so we can create the right type there.

Signed-off-by: Anton Lundin <glance@acc.umu.se>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Only calculate with he when he is present in event

Old gasswitch events only contains O2, so don't look at he part when
the event doesn't contain a He part.

Signed-off-by: Anton Lundin <glance@acc.umu.se>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Show sample time in the mouseover.

This is really nice to have when looking at specific coutures of a dive
or events.

Signed-off-by: Anton Lundin <glance@acc.umu.se>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>