Display liters with script el

Use script ell instead of 'l' for liters to avoid confusion with digit 1.
Let's hope that this glyph is available in the common fonts, otherwise
we'll have to revert it.

[Dirk Hohndel: split commit into two]

Signed-off-by: Robert C. Helling <helling@atdotde.de>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Planner: incease step size in deco ascends to 3 seconds

Triple time step in deco ascents to improve responsiveness of interactive
deco calculation.

[Dirk Hohndel: split commit into two]

Signed-off-by: Robert C. Helling <helling@atdotde.de>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Really display liters with script el

In commit 125ddd955c04 ("Display liters with script el") Robert only fixed
the C routine we use to show units. Strangely, we had a separately
implemented C++ function as well. Instead of implementing this in two
spots I now simply have the C++ function use the C function to do the
actual work and then wrap this into an easier to use (from UI code)
QString output.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Change character for liter in SAC values as well

And fix the bug that in the info overlay SAC was always given in metric
values. And try to reduce the number of places in which we calculate the
unit conversions...

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>