Make a guess at the cylinder description from the size and pressure

Make a guess at the cylinder description from the size and pressure

I'll want to also add a way to override/set the cylinder type: both
manually by just setting a size in liters, and by picking from some list
of standard cylinder sizes.

For example, it looks like most of my dives are marked as having
12-liter cylinders.  That is probably some default from Suunto Dive
Manager, or from whatever Dirk did.  It's almost certainly not right for
any of them: as far as I know, the standard cylinders for Lahaina Divers
(which is likely most of the warm water dives) are AL72's for air, and
AL80's for Nitrox.

That would be a 10L and a 11.1L tank respectively, afaik.  I don't know
what a 12-liter tank would be or where that size comes from.

Anyway, the LP85+ tank designation for some of the dives looks more
likely: that's one of the common sizes I've used for local dives.  So
the size of that thing is much more probably correct.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>