Do not hide ships when they cannot be placed.

Some methods in the Delegate classes were too much procedural to my
like. I don't see with good eyes a method that should return a bool
returning a pointer instead.

To get rid of this, Delegate::canAddShip() now returns bool and when we
need to get a pointer to the next ship to be placed, nextShip() -- which
became public -- does its job.

This is not everything, the coolest part of this commit is that now
sprites will turn red when a ship can't be placed and green when this is
not the case. Just like some RTS games do. :-)

Just between us, having no sprites at all wasn't very user friendly.

FEATURE: 308215
FIXED-IN: 4.13.1
GUI:
DIGEST: