Clarification on EAD and END meaning in Subsurface

As pointed out in commit 23ce727 by Dirk and remembered Jan, there are different
meanings for EAD and END depending on organisations.  Let's explain a bit the one
Subsurface has choosen,  as this is confusing, even while translating the acronyms.

Signed-off-by: Salvador Cuñat <salvador.cunat@gmail.com>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Fix units boxes in preference panel

The groupBox-es got renamed, and thus the unit-systems radio-buttons
was enabling/disabling the wrong buttons.

Signed-off-by: Anton Lundin <glance@acc.umu.se>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Rename the radio button to match label kgs->kg

Signed-off-by: Anton Lundin <glance@acc.umu.se>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Update the diffrent units when switching system

When switching between metric and imperial, we should also show that the
different units are switching too. This signals the greyed out
radio buttons to switch to the right system.

Fixes #347

Signed-off-by: Anton Lundin <glance@acc.umu.se>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Keep track of user requested minimum depth

When got auto-rescaling of the depth scale, always reset the depth scale
to what the profile would suggest. This introduces a concept of user
requested minimum witch we will update and not scale down to lower than.

Reported-by: Henrik Brautaset Aronsen <henrik@synth.no>
Signed-off-by: Anton Lundin <glance@acc.umu.se>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>