Remove obsolete slots

The .ui components were removed in commit 0c7a575f7b3b ("Rework on the
Equipment tab to make it look more Modern.") but the "automagic" slots
were still here.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Remove a compile warning

It's cleaner to make this a QString, anyeway.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Enable the weightsystem info and move the declarations to dive.h

Having the tank_info declared in models.cpp seemed unintuitive.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Add weightsystem delegate to enable editing of weightsystem

This is very much analogous to the way cylinders are implemented.
That means that just like with cylinders, if the user enters a new type
and hits 'tab' before hitting 'enter', Subsurface will crash.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Correctly add new weight / cylinder types, even when hitting 'tab'

We now detect if a weight / cylinder with this description exists and if
not add it on the fly. We also remember the additional values (weight and
size / workingpressure) for new entries and take the values for these
fields into account when autocompleting.

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