Properly implement the unsaved-changes flag(s). Since we currently have
two kinds of changes, there are two flags:
1) dive_list_changed in divelist.c marks non-undoable changes. This flag
is only cleared on save or load.
2) QUndoStack::isClean() is used to determine the state of undoable
changes. Every time the user returns to the state where they saved,
this flag is cleared.
Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>
This is copying the dive editing code. It uses an OO design with
virtual functions for getting and setting the values. It doesn't
use templates though, as both fields of strig type. This feels
a bit over-engineered, but it is 1) consistent with the dive edit
code and 2) the number / types of dive trip fields might increase.
Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>
