Change add_plan_to_notes() to operated on gasmix

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
More cleanup for planner.c

Remove unused variables and make the ifdef'ed out debug code work again.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
More conversions to gasmix

addStop, addGas and createSimpleDive.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Override the MinMaxAvgWidget tool tips for the depth instance.

Add new methods to the MinMaxAvgWidget class to allow us to override the
default tooltips of its min and max icons, and then uses these methods to
make the tooltips for the Stats tab Depth instance more descriptive.

See #521

Signed-off-by: Tim Wootton <tim@tee-jay.demon.co.uk>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Create simple non-thread-safe "gasname()" function

Every single user of the get_gas_name() function wanted to just use the
result to create a message or printout, and that made the interface a bit
cumbersome.

This adds a "gasname()" wrapper that returns a static buffer with the
result in it, which is neither pretty nor thread-safe, but is a much
simpler interface to work with.

Our dive planning isn't multi-threaded, so nothing should care.

[ This also converts a few open-coded gasname debug printouts to use the
  helper function, resulting in prettier printouts and less code ]

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>